CA1166173A - Hydraulic brake piston - Google Patents
Hydraulic brake pistonInfo
- Publication number
- CA1166173A CA1166173A CA000384706A CA384706A CA1166173A CA 1166173 A CA1166173 A CA 1166173A CA 000384706 A CA000384706 A CA 000384706A CA 384706 A CA384706 A CA 384706A CA 1166173 A CA1166173 A CA 1166173A
- Authority
- CA
- Canada
- Prior art keywords
- post
- outer cylinder
- rearward
- ribs
- pin
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D65/00—Parts or details
- F16D65/14—Actuating mechanisms for brakes; Means for initiating operation at a predetermined position
- F16D65/16—Actuating mechanisms for brakes; Means for initiating operation at a predetermined position arranged in or on the brake
- F16D65/22—Actuating mechanisms for brakes; Means for initiating operation at a predetermined position arranged in or on the brake adapted for pressing members apart, e.g. for drum brakes
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
- F16D2125/00—Components of actuators
- F16D2125/02—Fluid-pressure mechanisms
- F16D2125/06—Pistons
Landscapes
- Engineering & Computer Science (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Braking Arrangements (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A fluid dynamic piston, e.g. a hydraulic brake piston, has an outer cylinder having an open forward end and a closed rearward end and a post coaxially disposed within the outer cylinder and having an axial cavity in its forward end. The post extends axially from the outer cylinder's closed rearward end through at least a portion of the outer cylinder's axial length and circumferentially-spaced ribs extend radially between the post and the outer cylinder and axially from the outer cylinder's closed rear-ward end through at least a portion of the axial length of the annular space. The outer cylinder, the post and the ribs comprise synthetic material and the ribs have forward ends intersecting the post rearwardly of the outer cylinder's open forward end. An abutment is attached to the post's open forward end and comprises a pin having forward and rearward ends and a flange on the pin's for-ward end, the rearward end of the pin extending into the cavity to a depth no further rearward than the intersection of the ribs and the post.
A fluid dynamic piston, e.g. a hydraulic brake piston, has an outer cylinder having an open forward end and a closed rearward end and a post coaxially disposed within the outer cylinder and having an axial cavity in its forward end. The post extends axially from the outer cylinder's closed rearward end through at least a portion of the outer cylinder's axial length and circumferentially-spaced ribs extend radially between the post and the outer cylinder and axially from the outer cylinder's closed rear-ward end through at least a portion of the axial length of the annular space. The outer cylinder, the post and the ribs comprise synthetic material and the ribs have forward ends intersecting the post rearwardly of the outer cylinder's open forward end. An abutment is attached to the post's open forward end and comprises a pin having forward and rearward ends and a flange on the pin's for-ward end, the rearward end of the pin extending into the cavity to a depth no further rearward than the intersection of the ribs and the post.
Description
116~73 The invention relates to 2 hydraulic piston for use in automotive hydraulic bra~e systems an~ comprising a synthetic material.
Although an automotive hydraulic drum brake em-bodiment of the invention is disclosed, one skilled in the automotive brake art may well adapt the invention to other types of hydraulic or air-actuated brake systems.
Conventional hydraulic drum brakes for vehicles typically include two arcuate brake shoes slidably mounted in an end-to-end orientation on a staticnary backing plate affixed to the vehicle. The brake shoes have friction material affixed to their outer surfaces for engaging the inner surface of a rotatable drum upon which the vehicle wheel is generally mounted. ~rhe brake shoes have upper ends abutting opposed pistons of a hydraulic cylinder mounted on the backing plate. Typically, return springs keep the brake shoes in const~nt abutment with the pistons.
When hydraulic pressure is applied to the wheel cylinder, the pistons extend in opposite directions to urge the brake shoes outwardly against the inner surface of the brake drum. The return springs retract the brake shoes when the hydraulic pressure i, released, thereby freeing the drum to rotate.
Conventional wheel cylinders generally have one-piece metal pistons or, alternatively, two-piece pistons having a piston body with an abutment plug inserted into the outboard end (see Fig. 1) The abutment plug, which is generally hardened metal, serves as a bearing surface for engaging the upper ends oi the brake shoes. Metal pistons are relatively heavy, expensive to manufacture and subject to high rates of wear between the pistons and their mating surfaces. The need has thus arisen for a hydraulic brake piston that may be inexpensively manufactured from a lightweight material having a low coefficient of friction, that is compatible with commonly-used brake fluids, and that is capable of withstanding the high stresses and tem-peratures of brake operation while maintaining its dimen-sional integrity.
t 1 ~ 3 In accordance with the pres~nt invention, there is provided a fluid dynamic piston which comprises an outer cylinder having an open forward end and a closed rearward end, a post coaxially disposed within the outer cylinder and having an axial cavity in its forward end, the post extending axially from the outer cylinder's closed rearward end through at least a portic,n of the outer cylinder's axial length, a plurality of circumferentially-spaced ribs extend-ing radially between the post and the outer cylinder and extending axially from the outer cylinder's closed rearward end through at least a portion of the axial length of the annular space, the outer cylinder, the post and the ribs comprising synthetic material, the ribs having forward ends intersecting the post rearwardly of the outer cylinder's open forward end, and abutment means attached to the post's open forward end and comprising a pin having forward and rearwa~d ends and a flange on the pin's forward end, the rearward end of the pin extending into the cavity to a depth no further rearward than the intersection of the ribs and the post.
Fig. 1 is an overall view of a typical vehicle drum brake assembly with the wheel cylinder partially cut away to show a typical hydraulic piston known in the prior art.
Fig. 2 is a cross-sectional view of a typical hydraulic drum brake wheel cylinder assembly having a piston embodying the present invention.
Fig. 3 is an exploded cross-sectional elevation view of a preferred hydraulic piston embodying the present invention taken along line 3-3 of Fig. 4.
Fig. 4 is a forward end view of the preferred hydraulic piston embodying thle invention.
Figs. 5 through 10 are radial cross-sectional views of exemplary alternate embodiments of the present invention.
Referring to the drawings, where like elements are designated by like numeraLs, Fig. 1 illustrates a typical vehicle drum brake assembly 9 of the priOr art for .
~ ~fi~7~3 a vehicle wheel normally rotating in the direction indica-ted by arrow 10. Drum brake assembly 9 includes braking plate 11 onto which leading and trailing arcuate brake shoes 12]L and 12T respectively are slidably mounted. The brake shoes 12L and 12T have webs 13L and 13T supporting arcuate rims 14L and 14T, respectively, to which friction material sections 15L and 15T are affixed by any known means.
A prior art hydraulic wheel cylinder assembly 18 of the prior art is shown in Fig. 1 secured to backing plate 11 between upper brake shoe ends l9L and l9T. Return spring 20 includes hooks 21L and 21T engaging upper web apertures 22L and 22T, respectively, biasing brake shoes 12L and 12T toward wheel cylinder assembly 18. Anchor block 25 is rigidly attached to backing plate 11 between lower brake shoe ends 26L and 26T. Retaining spring 27 includes hooks 28L and 28T engaging lower shoe apertures 29L and 29T, respectively, urging lower brake shoe ends 26L and 26T toward each other in constant abutment with opposite sides of anchor block 25.
In operation, as hy~raulic pressure is applied to wheel cylinder assembly 1~, piston 16 extends to slidably urge leading brake shoe 12L outwardly. Lower shoe end 26L
rotates against anchor block 25, and friction material section 15L frictionally engages the inner surface of brake drum 30, thereby retarding the rotation of brake drum 30 and the vehicle wheel. The trailing brake shoe assembly operates similarly and simultaneously. Upon release of the hydraulic pressure, pistons 16 retract under the in-wardly-directed biasing force of return spring 20 which also urges brake shoes 12L and l~T to their original posi-tions, thereby freeing brake drum 30, and thus the vehicle wheel, to rotate.
Fig. 2 presents a cross-sectional view of wheel cylinder assembly 18, incorporating two pistons 32 which represent the preferred embod.;ment of the present invention.
Pistons 32 are positioned for opposed slidable movement within cylinder 31, forming hydraulic chamber 33 there-between. Elastomeric cups 34 act as hydraulic seals and . ~
i 1 ~fi ~ 73 abut the rearward surface of pis~ons 32, and cup expanders 35 abut the rearward sides of cups 34 and receive biasing spring 36. Dust boots 38 engage external grooves 39 of wheel cylinder assembly 18 and extend into cylin~er 31 to sealingly engage actuating pistons 32.
Piston 32 includes a cylindrical outer sleeve 45 having a closed rearward wall 46, an open forward end 47, inner surface 48, and outer surface 49. Post 50 is coaxially disposed within outer sleeve 45 and includes an outer cylindrical surface 51, internal cavity 52, cavity bottom 53, cavity opening 54, which is preferably chamfered, and cavity inner surface 55. Post 50 protrudes in a forward axial direction from rearward wall 46 and may, depending upon the particular brake mechanism design, extend beyond outer sleeve forward end 47. Post 50 has an external dia-meter that is smaller than the internal diameter of outersleeve 45 thereby forming annular space 56 therebetween.
Post outer surface 51 diverges at angle B, and cavity inner surface 55 converges at angle C, to form a frustoconical annular base portion 70 adjacent rearward wall 46. Base portion 70 allows the axial forces encounter-ed during brake operation to be more evenly distributed across rearward wall 46. Angle B lies within the range of 5 to 25 degrees, and is preferably 15 degrees. Angle C lies within the range of 30 to 90 degrees and is preferably 60 degrees.
Ribs 57 are circumferentially spaced within an-nular space 56 and extend between the inner surface 48 of outer sleeve 45 and the outer surface 51 of post 50. Ribs 57 preferably extend from piston rearward wall 46 along at least a portion of the axial length of post 50 to a point rearward of outer sleeve forward end 47. The forward ends 59 ~f ribs 57 preferably slope forwardly and outwardly from post 50 to forward end 47 of o~ter sleeve 45 and inter-secting the post 50 rearwardly of the open forward end 47 of the outer sleeve 45 as shown in Fig. 3, thus leaving a portion of annular space 56 open to form expansion space 58 between post 50 and the outer sleeve.
1 ~ fi6 ~ 73 Since existing synthetic resins of the day do not exhibit adequate surface load bearing characteristics, a metal abutment plug or cap is preferably included in the piston assembly to act as a bearing surface for the brake shoe ends 19L and l9T. Should resins be developed in the future that have such characteristics, the abutment plugs or caps in the preferred and alternate embodiments disclosed herein may be eliminated.
Abutment plug 37 in the preferred embodiment in-cludes flange 61 and pin 62. Pin 62 diverges in the rear-ward direction at angle A so as to provide a tight fit wheninserted into post cavity 52. Angle A normally lies within the range of one-half to two degrees, and is preferably one degree. The rearward end 63 of pin 62 may be provided with chamfer 64 for ease of insertion into cavity opening 54. Preferably, abutment plug 37 is pressed into post cavity 52 during assembly until its abutment flange 61 seats against the forward end 66 of post 50. Pin 62 projects into cavity 52 only to an axial depth equal to, or less than, the axial length of open expansion space 58. Thus any diametric expansion of post 50 caused by the force-fitting of abutment plug 37 into cavity 52 is not imparted to outer sleeve 45. Ribs 57 therefore provide radial structural reinforcement between post 50 and cylindrical outer sleeve 45 without causing an increase in the outside diameter of piston 32. Expansion space 58 also serves as an area for dust boot 38 (see Fig. 2) to sealingly engage post 50 and outer sleeve 45.
~ variation on the preferred embodiment of the invention may employ an alternate abutment plug having a pin of uniform diameter that does not cause expansion of the inner sleeve. The plug may be secured to the piston with any known adhesive to keep it in place during brake maintenance. Since such an abutment plug pin causes no expansion of the inner sleeve, the strengthening ribs may extend the full axial length of the post wi-thout resulting in expansion of the outer sleeve.
A further variation on the preferred embodiment ~!
I ~fifit7~
-- 6 ~
has an abutment cap that fits over the forward end of the post rather than an abutment plug that fits into a post cavity. Such a cap may be secured to the post with an ad-hesive as discussed above.
Piston 32 may be composed of any of several known thermoplastic or thermosetting resins that are compatible with commonly used hydraulic brake fluids and that exhibit suitable dimensional stability under the temperatures expected in the piston environment during brake operation.
Such temperatures may range from ambient to as high as 250F.
The resin may be reinforced with glass fibers, glass spheres, talc, carbon, or any other known organic or inorganic materials for added strength and dimensional stability.
Examples of a suitable material is glass-filled 66 nylon (such as FIBERFILL G 10/40) or glass-filled 612 nylon (such as FIBERFILL G 4/34 or G 4/45).
` The preferred embodiment as described herein has been successfully reduced to practice for a drum brake wheel cylinder with a nominal bore size of 17 millimeters. The piston is composed of glass-filled nylon and is compatible with the glycol-based hydraulic brake fluid currently used in the United States. After 250,000 hydraulic pressure cycles simulating braking applications, the pistons and cylinders showed appreciably less scuffing, abrasion and wear than did aluminum pistons of the prior art. Such re-duced wear is especially advantageous because such pistonsmay be used in aluminum wheel cylinders without costly anodizing of the cylinders.
Other synthetic materials, such a phenolic or reinforced epoxy resins, which are thermosetting resins, also provide the necessary compatibility with glycol-based brake fluid and may be expected to have adequate mechanical properties to meet the above~mentioned criteria. The use of silicone or mineral based brake fluids common in Europe may require the use of other synthetic resins that are com-patible with those fluids.
Since pistons embodying the present inventionmay be injection molded, one is given an infinite choice .": .s .
~ 1 66 ~ 7 3 of piston configurations and :Ls not ~ound by the cost and process limitations associated with the machining and fabrica-tion of other materials such as metals. Some of these choices are illustrated in Figs. 5 through 10 and represent examples of alternate embodiments of the present invention.
After examining these examples, further alternate embodi-ments of the present invention will undoubtedly occur to one skilled in the art.
In Fig. 5, piston 7:L has an inner member 72 co-axial with outer sleeve 45. In contrast with the cylin-drical post 50 of the preferred embodiment, inner member72 is "star-shaped" and includes a plurality of apexes or corners 73 circumferentially ,paced about its periphery.
The apexes 73 extend to join outer sleeve inner surface 48 and provide radial structural reinforcement between inner member 72 and the outer sleeve.
Piston 71 is shown in Fig. 5 having a coaxial cavity 74 for receiving an abutment plug. However, as with the preferred embodiment, piston 71 and any of the other alternate embodiments in Figs. 6 through 10 may have solid inner members or posts. In such cases, an abutment cap may be provided to fit over the forward end of the inner member or post, or alternatively an abutment disc may be mounted on the end of the inner member or post. Such an abutment disc may be recessed in an opening in the forward end or may be mounted such that its thickness axially pro-trudes from forward end.
Fig. 6 illustrates another example of an alternate embodiment of the present invention in which piston 76 in-cludes an inner post 77 having a rectangular cross-section.
Inner post 77 intersects with, and is attached to, outer sleeve inner surface 48 at its corners for radial reinforce-ment of the outer sleeve 45.
In Fig. 7, piston 7~ has an inner post 80 that is also rectangular in cross-section however, unlike that 35 of piston 76 in Fig. 6, inner post 80 intersects with, and attaches to, outer sleeve inner surface 48 along its entire width ~w) to provide radial reinforcement for outer sleeve 45.
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1 1 66~73 Fig. 8 illustrates piston 82 which has post mem-ber 83 that is '`cross-shaped". Post 83 has integral radial reinforcement extensions 84 which intersect and join with out:er sleeve inner surface 48 along their entire width (w).
Piston 82 is shown in Fig. 8 with adjacent radial extensions 84 preferably oriented substantially perpendicular to each other. However, adjacent radial extensions 84 may be oriented at angles other than 90 if such other angles are desirable or advantageous.
Figs. 9 and lO illustrate pistons 86 and 86' respectively having posts 87 and 87' respectively. Post 87 and 87' are both hexagonal in cross-section and have radial reinforcement spokes 88 and 88' respectively for radially reinforcing outer sleeve 45. Spokes 88 and 88' are circumferentially spaced about the periphery of p~s~t 87 and 87' and extend radially to intersect and join the outer sleeve inner surface 48 of pistons 86 and 86' respectively. In Fig. 9, spokes 88 radially extend from the intersections of the sides of the hexagonal cross-section of inner member 87, while spokes 88' in Fig. lO
radially extend from the flat portions of the sides of inner member 87'. Although Figs. 9 and lO show pistons with posts having a hexagonal cross-section, the piston of the present invention may have posts of other cross-sectional shapes if desirable or advantageous.
The foregoing descriptions represent merely exem-plary embodiments of the present invention. Various changes may be made in the arrangement and details of production of the embodiments shown and described without departing from the spirit and scope of 1he present invention.
~,~
. .
Although an automotive hydraulic drum brake em-bodiment of the invention is disclosed, one skilled in the automotive brake art may well adapt the invention to other types of hydraulic or air-actuated brake systems.
Conventional hydraulic drum brakes for vehicles typically include two arcuate brake shoes slidably mounted in an end-to-end orientation on a staticnary backing plate affixed to the vehicle. The brake shoes have friction material affixed to their outer surfaces for engaging the inner surface of a rotatable drum upon which the vehicle wheel is generally mounted. ~rhe brake shoes have upper ends abutting opposed pistons of a hydraulic cylinder mounted on the backing plate. Typically, return springs keep the brake shoes in const~nt abutment with the pistons.
When hydraulic pressure is applied to the wheel cylinder, the pistons extend in opposite directions to urge the brake shoes outwardly against the inner surface of the brake drum. The return springs retract the brake shoes when the hydraulic pressure i, released, thereby freeing the drum to rotate.
Conventional wheel cylinders generally have one-piece metal pistons or, alternatively, two-piece pistons having a piston body with an abutment plug inserted into the outboard end (see Fig. 1) The abutment plug, which is generally hardened metal, serves as a bearing surface for engaging the upper ends oi the brake shoes. Metal pistons are relatively heavy, expensive to manufacture and subject to high rates of wear between the pistons and their mating surfaces. The need has thus arisen for a hydraulic brake piston that may be inexpensively manufactured from a lightweight material having a low coefficient of friction, that is compatible with commonly-used brake fluids, and that is capable of withstanding the high stresses and tem-peratures of brake operation while maintaining its dimen-sional integrity.
t 1 ~ 3 In accordance with the pres~nt invention, there is provided a fluid dynamic piston which comprises an outer cylinder having an open forward end and a closed rearward end, a post coaxially disposed within the outer cylinder and having an axial cavity in its forward end, the post extending axially from the outer cylinder's closed rearward end through at least a portic,n of the outer cylinder's axial length, a plurality of circumferentially-spaced ribs extend-ing radially between the post and the outer cylinder and extending axially from the outer cylinder's closed rearward end through at least a portion of the axial length of the annular space, the outer cylinder, the post and the ribs comprising synthetic material, the ribs having forward ends intersecting the post rearwardly of the outer cylinder's open forward end, and abutment means attached to the post's open forward end and comprising a pin having forward and rearwa~d ends and a flange on the pin's forward end, the rearward end of the pin extending into the cavity to a depth no further rearward than the intersection of the ribs and the post.
Fig. 1 is an overall view of a typical vehicle drum brake assembly with the wheel cylinder partially cut away to show a typical hydraulic piston known in the prior art.
Fig. 2 is a cross-sectional view of a typical hydraulic drum brake wheel cylinder assembly having a piston embodying the present invention.
Fig. 3 is an exploded cross-sectional elevation view of a preferred hydraulic piston embodying the present invention taken along line 3-3 of Fig. 4.
Fig. 4 is a forward end view of the preferred hydraulic piston embodying thle invention.
Figs. 5 through 10 are radial cross-sectional views of exemplary alternate embodiments of the present invention.
Referring to the drawings, where like elements are designated by like numeraLs, Fig. 1 illustrates a typical vehicle drum brake assembly 9 of the priOr art for .
~ ~fi~7~3 a vehicle wheel normally rotating in the direction indica-ted by arrow 10. Drum brake assembly 9 includes braking plate 11 onto which leading and trailing arcuate brake shoes 12]L and 12T respectively are slidably mounted. The brake shoes 12L and 12T have webs 13L and 13T supporting arcuate rims 14L and 14T, respectively, to which friction material sections 15L and 15T are affixed by any known means.
A prior art hydraulic wheel cylinder assembly 18 of the prior art is shown in Fig. 1 secured to backing plate 11 between upper brake shoe ends l9L and l9T. Return spring 20 includes hooks 21L and 21T engaging upper web apertures 22L and 22T, respectively, biasing brake shoes 12L and 12T toward wheel cylinder assembly 18. Anchor block 25 is rigidly attached to backing plate 11 between lower brake shoe ends 26L and 26T. Retaining spring 27 includes hooks 28L and 28T engaging lower shoe apertures 29L and 29T, respectively, urging lower brake shoe ends 26L and 26T toward each other in constant abutment with opposite sides of anchor block 25.
In operation, as hy~raulic pressure is applied to wheel cylinder assembly 1~, piston 16 extends to slidably urge leading brake shoe 12L outwardly. Lower shoe end 26L
rotates against anchor block 25, and friction material section 15L frictionally engages the inner surface of brake drum 30, thereby retarding the rotation of brake drum 30 and the vehicle wheel. The trailing brake shoe assembly operates similarly and simultaneously. Upon release of the hydraulic pressure, pistons 16 retract under the in-wardly-directed biasing force of return spring 20 which also urges brake shoes 12L and l~T to their original posi-tions, thereby freeing brake drum 30, and thus the vehicle wheel, to rotate.
Fig. 2 presents a cross-sectional view of wheel cylinder assembly 18, incorporating two pistons 32 which represent the preferred embod.;ment of the present invention.
Pistons 32 are positioned for opposed slidable movement within cylinder 31, forming hydraulic chamber 33 there-between. Elastomeric cups 34 act as hydraulic seals and . ~
i 1 ~fi ~ 73 abut the rearward surface of pis~ons 32, and cup expanders 35 abut the rearward sides of cups 34 and receive biasing spring 36. Dust boots 38 engage external grooves 39 of wheel cylinder assembly 18 and extend into cylin~er 31 to sealingly engage actuating pistons 32.
Piston 32 includes a cylindrical outer sleeve 45 having a closed rearward wall 46, an open forward end 47, inner surface 48, and outer surface 49. Post 50 is coaxially disposed within outer sleeve 45 and includes an outer cylindrical surface 51, internal cavity 52, cavity bottom 53, cavity opening 54, which is preferably chamfered, and cavity inner surface 55. Post 50 protrudes in a forward axial direction from rearward wall 46 and may, depending upon the particular brake mechanism design, extend beyond outer sleeve forward end 47. Post 50 has an external dia-meter that is smaller than the internal diameter of outersleeve 45 thereby forming annular space 56 therebetween.
Post outer surface 51 diverges at angle B, and cavity inner surface 55 converges at angle C, to form a frustoconical annular base portion 70 adjacent rearward wall 46. Base portion 70 allows the axial forces encounter-ed during brake operation to be more evenly distributed across rearward wall 46. Angle B lies within the range of 5 to 25 degrees, and is preferably 15 degrees. Angle C lies within the range of 30 to 90 degrees and is preferably 60 degrees.
Ribs 57 are circumferentially spaced within an-nular space 56 and extend between the inner surface 48 of outer sleeve 45 and the outer surface 51 of post 50. Ribs 57 preferably extend from piston rearward wall 46 along at least a portion of the axial length of post 50 to a point rearward of outer sleeve forward end 47. The forward ends 59 ~f ribs 57 preferably slope forwardly and outwardly from post 50 to forward end 47 of o~ter sleeve 45 and inter-secting the post 50 rearwardly of the open forward end 47 of the outer sleeve 45 as shown in Fig. 3, thus leaving a portion of annular space 56 open to form expansion space 58 between post 50 and the outer sleeve.
1 ~ fi6 ~ 73 Since existing synthetic resins of the day do not exhibit adequate surface load bearing characteristics, a metal abutment plug or cap is preferably included in the piston assembly to act as a bearing surface for the brake shoe ends 19L and l9T. Should resins be developed in the future that have such characteristics, the abutment plugs or caps in the preferred and alternate embodiments disclosed herein may be eliminated.
Abutment plug 37 in the preferred embodiment in-cludes flange 61 and pin 62. Pin 62 diverges in the rear-ward direction at angle A so as to provide a tight fit wheninserted into post cavity 52. Angle A normally lies within the range of one-half to two degrees, and is preferably one degree. The rearward end 63 of pin 62 may be provided with chamfer 64 for ease of insertion into cavity opening 54. Preferably, abutment plug 37 is pressed into post cavity 52 during assembly until its abutment flange 61 seats against the forward end 66 of post 50. Pin 62 projects into cavity 52 only to an axial depth equal to, or less than, the axial length of open expansion space 58. Thus any diametric expansion of post 50 caused by the force-fitting of abutment plug 37 into cavity 52 is not imparted to outer sleeve 45. Ribs 57 therefore provide radial structural reinforcement between post 50 and cylindrical outer sleeve 45 without causing an increase in the outside diameter of piston 32. Expansion space 58 also serves as an area for dust boot 38 (see Fig. 2) to sealingly engage post 50 and outer sleeve 45.
~ variation on the preferred embodiment of the invention may employ an alternate abutment plug having a pin of uniform diameter that does not cause expansion of the inner sleeve. The plug may be secured to the piston with any known adhesive to keep it in place during brake maintenance. Since such an abutment plug pin causes no expansion of the inner sleeve, the strengthening ribs may extend the full axial length of the post wi-thout resulting in expansion of the outer sleeve.
A further variation on the preferred embodiment ~!
I ~fifit7~
-- 6 ~
has an abutment cap that fits over the forward end of the post rather than an abutment plug that fits into a post cavity. Such a cap may be secured to the post with an ad-hesive as discussed above.
Piston 32 may be composed of any of several known thermoplastic or thermosetting resins that are compatible with commonly used hydraulic brake fluids and that exhibit suitable dimensional stability under the temperatures expected in the piston environment during brake operation.
Such temperatures may range from ambient to as high as 250F.
The resin may be reinforced with glass fibers, glass spheres, talc, carbon, or any other known organic or inorganic materials for added strength and dimensional stability.
Examples of a suitable material is glass-filled 66 nylon (such as FIBERFILL G 10/40) or glass-filled 612 nylon (such as FIBERFILL G 4/34 or G 4/45).
` The preferred embodiment as described herein has been successfully reduced to practice for a drum brake wheel cylinder with a nominal bore size of 17 millimeters. The piston is composed of glass-filled nylon and is compatible with the glycol-based hydraulic brake fluid currently used in the United States. After 250,000 hydraulic pressure cycles simulating braking applications, the pistons and cylinders showed appreciably less scuffing, abrasion and wear than did aluminum pistons of the prior art. Such re-duced wear is especially advantageous because such pistonsmay be used in aluminum wheel cylinders without costly anodizing of the cylinders.
Other synthetic materials, such a phenolic or reinforced epoxy resins, which are thermosetting resins, also provide the necessary compatibility with glycol-based brake fluid and may be expected to have adequate mechanical properties to meet the above~mentioned criteria. The use of silicone or mineral based brake fluids common in Europe may require the use of other synthetic resins that are com-patible with those fluids.
Since pistons embodying the present inventionmay be injection molded, one is given an infinite choice .": .s .
~ 1 66 ~ 7 3 of piston configurations and :Ls not ~ound by the cost and process limitations associated with the machining and fabrica-tion of other materials such as metals. Some of these choices are illustrated in Figs. 5 through 10 and represent examples of alternate embodiments of the present invention.
After examining these examples, further alternate embodi-ments of the present invention will undoubtedly occur to one skilled in the art.
In Fig. 5, piston 7:L has an inner member 72 co-axial with outer sleeve 45. In contrast with the cylin-drical post 50 of the preferred embodiment, inner member72 is "star-shaped" and includes a plurality of apexes or corners 73 circumferentially ,paced about its periphery.
The apexes 73 extend to join outer sleeve inner surface 48 and provide radial structural reinforcement between inner member 72 and the outer sleeve.
Piston 71 is shown in Fig. 5 having a coaxial cavity 74 for receiving an abutment plug. However, as with the preferred embodiment, piston 71 and any of the other alternate embodiments in Figs. 6 through 10 may have solid inner members or posts. In such cases, an abutment cap may be provided to fit over the forward end of the inner member or post, or alternatively an abutment disc may be mounted on the end of the inner member or post. Such an abutment disc may be recessed in an opening in the forward end or may be mounted such that its thickness axially pro-trudes from forward end.
Fig. 6 illustrates another example of an alternate embodiment of the present invention in which piston 76 in-cludes an inner post 77 having a rectangular cross-section.
Inner post 77 intersects with, and is attached to, outer sleeve inner surface 48 at its corners for radial reinforce-ment of the outer sleeve 45.
In Fig. 7, piston 7~ has an inner post 80 that is also rectangular in cross-section however, unlike that 35 of piston 76 in Fig. 6, inner post 80 intersects with, and attaches to, outer sleeve inner surface 48 along its entire width ~w) to provide radial reinforcement for outer sleeve 45.
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1 1 66~73 Fig. 8 illustrates piston 82 which has post mem-ber 83 that is '`cross-shaped". Post 83 has integral radial reinforcement extensions 84 which intersect and join with out:er sleeve inner surface 48 along their entire width (w).
Piston 82 is shown in Fig. 8 with adjacent radial extensions 84 preferably oriented substantially perpendicular to each other. However, adjacent radial extensions 84 may be oriented at angles other than 90 if such other angles are desirable or advantageous.
Figs. 9 and lO illustrate pistons 86 and 86' respectively having posts 87 and 87' respectively. Post 87 and 87' are both hexagonal in cross-section and have radial reinforcement spokes 88 and 88' respectively for radially reinforcing outer sleeve 45. Spokes 88 and 88' are circumferentially spaced about the periphery of p~s~t 87 and 87' and extend radially to intersect and join the outer sleeve inner surface 48 of pistons 86 and 86' respectively. In Fig. 9, spokes 88 radially extend from the intersections of the sides of the hexagonal cross-section of inner member 87, while spokes 88' in Fig. lO
radially extend from the flat portions of the sides of inner member 87'. Although Figs. 9 and lO show pistons with posts having a hexagonal cross-section, the piston of the present invention may have posts of other cross-sectional shapes if desirable or advantageous.
The foregoing descriptions represent merely exem-plary embodiments of the present invention. Various changes may be made in the arrangement and details of production of the embodiments shown and described without departing from the spirit and scope of 1he present invention.
~,~
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Claims (10)
1. A fluid dynamic piston comprising:
an outer cylinder having an open forward end and a closed rearward end;
a post coaxially disposed within said outer cylin-der and having an axial cavity in its forward end;
said post extending axially from the outer cy-linder's closed rearward end through at least a portion of the outer cylinder's axial length;
a plurality of circumferentially-spaced ribs ex-tending radially between said post and said outer cylinder and extending axially from the outer cylinder's closed rear-ward end through at least a portion of the axial length of said annular space;
the outer cylinder, the post and the ribs com-prising synthetic material;
said ribs having forward ends intersecting said post rearwardly of the outer cylinder's open forward end;
and abutment means attached to the post's open for-ward end and comprising a pin having forward and rearward ends and a flange on said pin's forward end, said rearward end of the pin extending into said cavity to a depth no further rearward than the intersection of said ribs and said post.
an outer cylinder having an open forward end and a closed rearward end;
a post coaxially disposed within said outer cylin-der and having an axial cavity in its forward end;
said post extending axially from the outer cy-linder's closed rearward end through at least a portion of the outer cylinder's axial length;
a plurality of circumferentially-spaced ribs ex-tending radially between said post and said outer cylinder and extending axially from the outer cylinder's closed rear-ward end through at least a portion of the axial length of said annular space;
the outer cylinder, the post and the ribs com-prising synthetic material;
said ribs having forward ends intersecting said post rearwardly of the outer cylinder's open forward end;
and abutment means attached to the post's open for-ward end and comprising a pin having forward and rearward ends and a flange on said pin's forward end, said rearward end of the pin extending into said cavity to a depth no further rearward than the intersection of said ribs and said post.
2. A fluid dynamic piston according to claim 1, wherein said post further includes a frustoconical annular base portion axially adjacent said outer cylinder's closed rearward end, said base portion diverging rearwardly to intersect said outer cylinder's closed rearward end.
3. A fluid dynamic piston according to claim 1, wherein said rearward end of the pin diverges in the rearward direction thereof.
4. A fluid dynamic piston according to claim 1, 2 or 3, wherein said forward ends of said ribs slope rearwardly away from the outer cylinder's open forward end.
5. A fluid dynamic piston according to claim 2, wherein said rearward end of the pin diverges in the rearward direction thereof and said forward ends of said ribs slope rearwardly away from the outer cylinder's open forward end.
6. A piston-activated vehicle brake having a fluid dynamic piston comprising:
an outer cylinder having an open forward end and a closed rearward end;
a post coaxially disposed within said outer cylin-der and having an axial cavity in its forward end;
said post extending axially from the outer cylin-der's closed rearward end through at least a portion of the outer cylinder's axial length;
a plurality of circumferentially-spaced ribs ex-tending radially between said post and said outer cylinder and extending axially from the outer cylinder's closed rear-ward end through at least a portion of the axial length of said annular space;
the outer cylinder, the post and the ribs compris-ing synthetic material;
said ribs having forward ends intersecting said post rearwardly of the outer cylinder's open forward end;
and abutment means attached to the post's open for-ward end and comprising a pin having forward and rearward ends and a flange on said pin's forward end, said rearward end of the pin extending into said cavity to a depth no further rearward than the intersection of said ribs and said post.
an outer cylinder having an open forward end and a closed rearward end;
a post coaxially disposed within said outer cylin-der and having an axial cavity in its forward end;
said post extending axially from the outer cylin-der's closed rearward end through at least a portion of the outer cylinder's axial length;
a plurality of circumferentially-spaced ribs ex-tending radially between said post and said outer cylinder and extending axially from the outer cylinder's closed rear-ward end through at least a portion of the axial length of said annular space;
the outer cylinder, the post and the ribs compris-ing synthetic material;
said ribs having forward ends intersecting said post rearwardly of the outer cylinder's open forward end;
and abutment means attached to the post's open for-ward end and comprising a pin having forward and rearward ends and a flange on said pin's forward end, said rearward end of the pin extending into said cavity to a depth no further rearward than the intersection of said ribs and said post.
7. A piston-activated vehicle brake according to claim 6, wherein said post further includes a frusto-conical annular base portion axially adjacent said outer cylinder's closed rearward end, said base portion diverging rearwardly to intersect said outer cylinder's closed rear-ward end.
8. A piston-activated vehicle brake according to claim 6, wherein said rearward end of the pin diverges in the rearward direction thereof.
9. A piston-activated vehicle brake according to claim 6, 7 or 8, wherein said forward ends of said ribs slope rearwardly away from the outer cylinder's open for-ward end.
10. A piston-activated vehicle brake according to claim 6, wherein said rearward end of the pin diverges in the rearward direction thereof and said forward ends of said ribs slope rearwardly away from the outer cylinder's open forward end.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US18228180A | 1980-08-28 | 1980-08-28 | |
| US182,281 | 1980-08-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1166173A true CA1166173A (en) | 1984-04-24 |
Family
ID=22667793
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000384706A Expired CA1166173A (en) | 1980-08-28 | 1981-08-27 | Hydraulic brake piston |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5773244A (en) |
| AR (1) | AR226609A1 (en) |
| BR (1) | BR8105483A (en) |
| CA (1) | CA1166173A (en) |
| DE (1) | DE3134055A1 (en) |
| FR (1) | FR2489462B1 (en) |
| GB (1) | GB2082728B (en) |
| MX (1) | MX153781A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR840003747A (en) * | 1982-03-12 | 1984-09-15 | 죤 밋첼 맥그라드 | Wheel Cylinder for Drum Brake |
| JPS58151743U (en) * | 1982-04-06 | 1983-10-11 | アイシン精機株式会社 | Piston for cylinder device |
| AT395047B (en) * | 1990-11-21 | 1992-08-25 | Reisner & Wolff Eng | POT-LIKE HYDRAULIC CYLINDER |
| DE19520670A1 (en) * | 1995-02-02 | 1996-08-08 | Teves Gmbh Alfred | Automatic braking system piston design in vehicle |
| EP0846891A1 (en) * | 1996-12-05 | 1998-06-10 | Borg-Warner Automotive, Inc. | Hydraulic tensioner with plastic body and piston |
| JP2016205485A (en) * | 2015-04-20 | 2016-12-08 | 曙ブレーキ工業株式会社 | Piston for disc brake device |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR885843A (en) * | 1941-09-18 | 1943-09-27 | Teves Gmbh Alfred | Piston for hydraulic systems |
| ZA727860B (en) * | 1971-12-01 | 1973-07-25 | Girling Ltd | Improvements in pistons |
| JPS5328374B2 (en) * | 1971-12-13 | 1978-08-14 | ||
| GB1551238A (en) * | 1975-09-18 | 1979-08-30 | Lucas Industries Ltd | Disc brake operating piston |
| CA1071549A (en) * | 1977-03-25 | 1980-02-12 | Richard T. Burnett | Drum brake and adjustment therefor |
| CA1084431A (en) * | 1977-09-15 | 1980-08-26 | Donald D. Johannesen | Hydraulic actuator for a drum brake |
-
1981
- 1981-08-27 BR BR8105483A patent/BR8105483A/en not_active IP Right Cessation
- 1981-08-27 MX MX18892081A patent/MX153781A/en unknown
- 1981-08-27 FR FR8116377A patent/FR2489462B1/en not_active Expired
- 1981-08-27 CA CA000384706A patent/CA1166173A/en not_active Expired
- 1981-08-28 AR AR28658181A patent/AR226609A1/en active
- 1981-08-28 GB GB8126386A patent/GB2082728B/en not_active Expired
- 1981-08-28 DE DE19813134055 patent/DE3134055A1/en not_active Withdrawn
- 1981-08-28 JP JP56134339A patent/JPS5773244A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| MX153781A (en) | 1987-01-09 |
| BR8105483A (en) | 1982-05-11 |
| GB2082728B (en) | 1984-06-27 |
| JPS5773244A (en) | 1982-05-07 |
| AR226609A1 (en) | 1982-07-30 |
| FR2489462B1 (en) | 1987-10-09 |
| FR2489462A1 (en) | 1982-03-05 |
| DE3134055A1 (en) | 1982-04-22 |
| GB2082728A (en) | 1982-03-10 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |