FR2489462A1 - HYDRAULIC BRAKE SYSTEM - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A HYDRAULIC PISTON 32 SUITABLE FOR PARTICULARLY IN BRAKE SYSTEMS FOR AUTOMOBILES, WHICH CAN BE MANUFACTURED FROM RESIN ARMED WITH FIBERS FOLLOWING KNOWN INJECTION MOLDING TECHNIQUES. THE PISTON INCLUDES A CYLINDER 18 CLOSED AT ONE OF THE ENDS, AND A MEANS 37, OF LOAD SUPPORT, COAXIAL, RADIAL REINFORCEMENT, CENTRAL, EXTENDS FROM THE CLOSED END AND FOLLOWING THE LENGTH OF THE CYLINDER SO AS TO TRANSMIT AXIAL FORCES TO THE BRAKE COMPONENTS.

Description

Hydraulic brake system

  The present invention relates to a hydraulic piston

  than for a hydraulic automobile braking system,

  made of synthetic material.

  Although a hydraulic drum brake for motor vehicles is described in the present invention, those skilled in the art

  art can adapt it to other types of brake systems

hydraulic or pneumatic swimming.

  In typical hydraulic drum brakes for vehicles, two arc-shaped brake pads are fitted

  end to end so as to slide on a fixed support plate assu-

  throws to the vehicle. The outer surface of the brake pads. includes a friction material which comes into contact with the inner surface of a rotating drum on which the vehicle wheel is generally mounted. The pads have upper ends abutting opposite pistons of a hydraulic cylinder mounted on their support plate. Typically, return springs

  keep the pads in constant contact with the pistons.

  When hydraulic pressure is applied to the

  wheel cylinder, pistons extend in directions

  opposite positions so as to urge the skates towards the ex-

  inside and against the inner surface of the drum. The res-

  booster spells cause brake pads to be withdrawn

  when the hydraulic pressure is released, it results

  the drum can rotate freely.

  Classic wheel cylinders generally have

  monoblock metal pistons or, alternatively, pistons

  tones in two pieces consisting of a body with a cap

  stopper inserted in the outer end (see figure 1).

  The stopper plug, which is generally made of case-hardened metal, serves as a bearing surface for the engagement of the upper ends of the brake pads. Metal pistons are relatively heavy, have a high manufacturing cost and are subject to significant wear rates on their paired surfaces. There is therefore a need for a hydraulic brake piston which can be manufactured at

  low cost with a light material having a low coefficient

  friction friction, which is compatible with the brake fluids generally used, and capable of withstanding the high stresses and temperatures encountered during the operation of the brake while maintaining its dimensions intact. The present invention relates to a piston of

  improved hydraulic brake, made of a thermo resin

  thermoplastic resistant to high temperatures and reinforced with an organic or mineral material. The piston preferably comprises an external sleeve or cylinder comprising a closed rear wall with a coaxial support support element.

  load extending from the wall through the cylinder.

  A particular embodiment of the piston

  takes circumferential distant reinforcing ribs

  tally from each other and extending in space

  ring between the outer sleeve or cylinder and the element

  load support ment. The load support member projects from the rear wall and preferably extends beyond the open end of the outer sleeve. A cemented metal abutment surface is preferably attached to the front end of the load support member so that it comes into contact with elements of the brake shoe.

  The present invention will be clearly understood on reading

  re of the following description made in relation to

attached drawings, in which:

  Figure 1 is an overall view of a drum brake.

  typical bour of a vehicle, the wheel cylinder being

  partially punctured so as to show a hydraulic piston

typical prior art;

  Figure 2 is a sectional view of a typical cylinder

  as a hydraulic drum brake wheel, comprising a piston according to the present invention; FIG. 3 is a sectional elevation view,

  exploded, of a particular hydraulic piston according to the present

  te invention, taken along line 3-3 of Figure 4 Figure 4 is a front end view of the particular hydraulic piston of the present invention; Figures 5 to 10 are views in radial section

  other embodiments of the present invention.

  In connection with the drawings, o elements identi-

  they are designated by the same references, Figure I

  represents a typical brake assembled 9 to drum for vehicle

  cule of the prior art which is intended for a vehicle wheel

  This normally turns in the direction of the arrow 10. The assembled brake 9 comprises a support plate 11 on which front and rear brake pads in the shape of an arc - 12L and 12T, respectively are mounted to slide. The pads 12L and 12T have webs 13L and 13T supporting

  arc-shaped rims- 14L and 14T, respectively, on the-

  which are fixed by means known to the sections of

friction material 15L and 15T.

  A hydraulic cylinder for prior art wheel

  Laughter 18 is shown in Figure 1 as being attached to the plate.

  that support 11 between the upper ends 19L and 19T of the brake pads. A return spring 20 comprises hooks 21L and 21T engaged in openings 22L and 22T of the upper webs, respectively, urging the pads 12L and 12T towards the cylinder 18. An anchoring block 25 is

  rigidly fixed to the plate 11 between the lower ends

  res 26L and 26T of the brake pads. A retaining spring

  27 includes hooks 28L and 28T engaged in openings

  lower res of pads 29L and 29T, respectively, urging the lower ends 26L and 26T of the pads towards each other so that they are in constant contact with

  opposite ends of block 25.

  In operation, during application of the pres-

  hydraulic pressure to the assembly 18, the piston 16 extends from

  so as to stress outwards the front shoe 12L.

  The end 26L of the lower shoe rotates against the block 25, and the section 15L of friction material comes into frictional contact with the internal surface of the drum 30, whence results in a braking of the rotation of the drum 30 and of the vehicle wheel. The assembly comprising the front pad operates in the same way and simultaneously. When

  release of hydraulic pressure, pistons 16 re-

  come back under the effect of the inwardly directed biasing force exerted by the brake return spring, which also biases the pads 12L and 12T to return them to their original position, resulting in a

  free rotation of the drum 30, and of the vehicle wheel.

  FIG. 2 represents a sectional view of the whole

  ble 18 comprising the wheel cylinder, which incorporates two

  pistons 32 which represent the particular embodiment

  of the present invention. The pistons 32 are placed so as to slide in opposite directions inside a

  cylinder 31, creating between them a hydraulic chamber 33.

  Elastomer cups 34 act as hydraulic seals

  ques and abut against the rear surface of the pistons 32, and cup extension elements 35 abut against the rear side of the cups 34 and receive a biasing spring 36. Anti-mud envelopes 38 are engaged

  in external grooves 39 of the assembly 18 and extend

  tooth in cylinder 31 so as to be in tight contact

with the actuating pistons 32.

  The piston 32 includes an external cylindrical sleeve

  laughing 45 having a closed rear wall 46, an open front end 47, an internal surface 48, and an external surface 49. A pillar 50 is arranged coaxially inside the sleeve 45 and comprises an external cylindrical surface 51, a inner cavity 52, a cavity bottom 53, a cavity opening 54, which is preferably chamfered, and an inner cavity surface 55. The pillar 50 projects in a forward axial direction from the rear wall 46 and can , according to the particular design of the brake mechanism, extend beyond the front end 47 of the outer sleeve. Pillar 50 a

  an outside diameter which is smaller than the inner diameter

  inside of sleeve 45, from which an annular space results

56 between them.

  The outer surface 51 of the pillar diverges at an angle B, and the inner surface 55 of the cavity converges

  at an angle C, so as to form a base part an-

  ring 70 of frustoconical shape which is contiguous to the rear wall 46. The base part 70 allows a more uniform distribution of the axial forces encountered during the braking operation on the rear wall 46. The angle B is included in the range 5 -25, is preferably 150. The angle C is cmpris

  in the range 30-90, and is preferably 60.

  Ribs 57 are circumferentially spaced from each other within the annular space 56 and extend between the interior surface 48 of the sleeve 45 and

  the outer surface 51 of the pillar 50. The ribs 57 extend

  tooth preferably from the rear wall 46 of the pillar to a point located behind the front end 47 of the outer sleeve. The front parts 59 of the ribs 57 are preferably sloping forward and outward from the pillar 50 to the front end 47 of the sleeve 45, thus leaving part of the space 56 open so as to form an expansion space 58 between the pillar 50 and the

outer sleeve.

  As current synthetic resins do not have load bearing characteristics

  suitable surface, a stopper or stopper cap

  metal is preferably included in the set comprising

  both the pistons so as to act as a bearing surface for the ends 19L and 19T of the brake pads. In the case where resins would be developed in the future having the preceding characteristics, the attached parts or abutment caps used in the particular embodiment of the present invention and in its variants

could be eliminated.

  The plug 37 of the particular embodiment of

  the present invention comprises a flange 61 and an axis 62.

  The axis 62 diverges in the forward direction at an angle A so as to ensure a tight fitting after insertion

  in the cavity 52. The angle A is normally between

  half and two degrees, and is preferably one degree.

  The rear end 63 of the axis 62 may include a chan-

  brake 64 so as to facilitate its insertion into the opening 54 of the cavity. Preferably, the plug 37 is pressed into the cavity 52 during assembly until its rim 61 is seated against the front end 66 of the pillar 50. The axis 62 is not protruding in the cavity 52 only over an axial depth equal to or less than the axial length of the expansion space 58. Thus any diametrical expansion of the pillar 50 caused by the forced mounting of the plug 37 in the cavity 52 is not imparted to the sleeve

  exterior 45. The ribs 57 therefore provide a reinforcement

  radial structural forcing between the pillar 50 and the external cylindrical sleeve 45 without causing an increase in the external diameter of the piston 32. The space 58 also serves as a reception surface for a dust-proof envelope 38 (see FIG. 2) which comes in waterproof contact with the abutment

and the outer sleeve 45.

  A variant of the particular embodiment of the present invention can use another stopper plug having an axis of uniform diameter which does not cause any expansion of the inner sleeve. The plug can be fixed to the piston with a known glue so as to keep it in place during maintenance of the brake. Like this type of axis

  plug does not cause expansion of the inner sleeve

  laughing, the reinforcing ribs can extend over the entire axial length of the pillar without there being

expansion of the outer sleeve.

  Another variant of the particular embodiment

  of the present invention is a stopper plug which

  mounts on the front end of the pillar instead of

  ter in a pillar cavity. Such a plug can be

  fixed to the pillar by an adhesive as described above

demment.

  The piston 32 can be made of a thermosetting resin.

  plastic or thermosetting which is compatible with

  commonly used hydraulic brake fluids which

  a dimensional stability suitable for temperatures

  tures encountered in the environment of the piston during

  braking operations. These temperatures can be

  its between room temperature and a temperature

  winning 1200C. The resin can be reinforced with glass fibers, glass spheres, talc, carbon, or any other organic or mineral material giving resistance

  mechanical and additional dimensional stability.

  Examples of suitable materials are the material called Nylon 66 reinforced with glass fiber (such as the material known as FIBERFILL G 10/40) or the material known as Nylon 612 reinforced with glass fiber (such as the material known as FIBERFILL G 4 / 34

or G 4/45).

  The particular embodiment which has just been de-

  crit has been successfully used in a wheel cylinder at

  drum brake with a nominal bore of 17 mm. The pis-

  tone was made of material called nylon reinforced with fibers

  of glass and is compatible with hydraulic brake fluid

  based on glycol commonly used in the United States of America. After 250,000 hydraulic pressure cycles

  simulating braking operations, pistons and cy-

  lindres showed no signs of friction,

Z489462

  abrasion and wear that are encountered in the aluminum pistons of the prior art. Such a reduction in wear is particularly advantageous since pistons of this nature can be used in aluminum wheel cylinders without having to carry out costly anodization.

cylinders.

  Other synthetic materials, such as resi-

  phenolic or reinforced epoxy, which are resins

  thermosets, are also compatible with fluid

  glycol-based brake pads and it is believed that they have mechanical properties which satisfy the criteria mentioned above. The use of brake fluids based

  of silicones or minerals, common in Europe, may require

  site the use of other compatible synthetic resins

with these fluids.

  Since the pistons of the present embodiment

  The invention can be injection molded, there is an infinite choice in the shapes of these pistons and we are not bound by the cost and procedural limitations associated with the machining and manufacturing of other materials such as metals. Some of these choices are shown in Figures 5 to 10, which are examples

  other embodiments of the present invention.

  After examining these examples, other embodiments

  of the present invention will no doubt come to the es

took from the skilled person.

  In FIG. 5, the piston 71 comprises an internal element 72 coaxial with the external sleeve 45. By contrast

  with the cylindrical pillar 50 of the particular embodiment

  tion of the present invention, the inner member 72 has the shape of a star and comprises a plurality of vertices or corners 73 circumferentially distant from each other around its periphery. The vertices 73 extend so as to join the inner surface 48 of the outer sleeve and provide radial structural reinforcement between the element

72 and the outer sleeve.

  The piston 71 of Figure 5 has a cavity

  coaxial 74 intended to receive a stopper stopper. However

  as in the case of the particular embodiment

  of the invention, the piston 71 and the other variants shown

  shown in Figures 6 to 10 may include elements

  massive interior pillars. In this case, a stopper plug can be provided which is mounted on the front end of the element or internal pillar, or alternatively a stopper disc can be mounted on the end of the element or

  inner pillar. Such a disc can be received in one or-

  groove made in the front end or can be mounted so that its thickness is axially projecting from

front end.

  FIG. 6 shows another example of an alternative embodiment of the present invention, where the piston 76 comprises an internal pillar 77 having a shape in rectangular section. The pillar 77 intersects the inner surface 48 of the outer sleeve, to which it is fixed at its angles

  so as to radially reinforce the sleeve 45.

  In figure 7, the piston 79-has an internal pillar

  laughter 80 which also has a rectangular cross-sectional shape; however, unlike piston 76 in Figure 6, the

  pillar 80 cuts the interior surface 48 of the outer sleeve

  laughing, to which it is fixed along its entire width (w) so as to ensure a radial reinforcement of the

sleeve 45.

  FIG. 8 represents a piston 82 which comprises a pillar element 83 having the shape of a cross. Pillar 83 has one-piece radial reinforcing portions 84 which intersect the inner surface 48 of the outer sleeve

  and join it over its entire width (w). The pis-

  tone 82 is represented in figure 8 with radial parts

  contiguous 84 preferably oriented so as to be sensitive

  clearly perpendicular to each other. However, the parts 84 can be oriented at angles

  other than 90 if such angles are desirable or pre-

feel an interest.

  Figures 9 and 10 show pistons 86 and

  86 ', respectively comprising pillars 87 and 87' respectively

  tively. The pillars 87 and 871 have a hexagonal shape in section and have radial reinforcing spokes 88 and 88 'respectivelyi intended to radially reinforce the outer sleeve 45. The spokes 88 and 88' are distant

  circumferentially from each other around the peri-

  and extend radially so as to join the inner surface 48 of the outer sleeve of the pistons 86 and 86 ', respectively. In FIG. 9, the spokes 48 extend radially from the points of intersection of the sides of the hexagonal section of the internal element 87,

  while the spokes 88 'of FIG. 10 extend radially-

  from the flat parts of the sides of the inner element

  laughing 87 '. Although FIGS. 9 and 10 show pistons with pillars having a hexagonal section, the piston of the present invention can have pillars having a section of another shape if it is considered that this is

desirable or advantageous.

  The present invention is not limited to the exemplary embodiments which have just been described, it is on the contrary susceptible of variants and modifications which

will appear to those skilled in the art.

Claims (6)

RESELL ICAT IONS   1. Dynamic piston actuated by fluid, characterized in that it coemrends a cylinder having a closed end, a cylinder reinforcement means extending axially from the closed end over at least part of the axial length of the cylinder, this means reinforcement ending with a stop means, from which it follows that the axial forces are transmitted from the closed end of the cylinder by means of stop.   2. Piston according to claim 1, characterized in   that the reinforcing means comprises a deflected projection   ness an annular space between the cylinder and the projection, a plurality of ribs extending between the cylinder and the projection.   3. Vehicle brake actuated by a piston or at least one piston, in response to dynamic forces exerted by a fluid, slides inside a cylinder to actuate the brake, characterized in that the piston comprises a cylinder having a closed end, a load support pillar means which extends from the closed end along the axial length of the cylinder, whence it follows that the means   abutment provides radial reinforcement of the cylinder and   puts the dynamic forces of the fluid to the operating elements brake.   4. Dynamic piston actuated by fluid, characterized in that it supports a cylinder- exterior having.-A front end open and a rear end closed coaxial pillar inside the exterior cylinder-and having an axial cavity at its front end , this pillar extending axially from the closed rear end of the outer cylinder on at   minus part of the axial length of the cylinder, for-   thus an annular space between the pillar and the cylinder   exterior, a plurality of circumferential remote ribs   tially from each other and extending radially between the pillar and the outer cylinder and extending axially between the closed rear end of the outer cylinder over at least part of the axial length of the annular space, these ribs being in slope backwards away from the open front end of the outer cylinder and cutting the pillar at the rear of this front end, and a stop means fixed to this front end. 5. Piston according to claim 4, characterized in   which the pillar further comprises an annular base part   frustoconical strip contiguous to the closed rear end of the outer cylinder, this base part diverging towards the rear so as to cut the closed rear end of the outer cylinder.   6. Piston according to claim 5, characterized in   that the stop means comprises an axis having extremi   front and rear tees and a flange on the front end, the rear end of the axis extending into the cavity to a depth not exceeding the intersection of the ribs and pillar. -