FR2555689A1 - PLASTIC SHOCK ABSORBER - Google Patents

Abstract

THIS SHOCK ABSORBER HAS A BODY 11 IN PLASTIC MATERIAL, A PISTON 17 MOUNTED IN THIS BODY, A PLASTIC MATERIAL 22, FOR EXAMPLE A FOAM OF PLASTIC MATERIAL WITH CLOSED ALVEOLES LODGE IN THE BODY, THE BODY AND THE SAID FOAM OF PLASTIC MATERIAL WITH FASTENED ALVEOLES CLOSE COEFFICIENTS SO THAT THE SHOCK ABSORBING CHARACTERISTICS ARE SENSITIVELY CONSTANT OVER A RELATIVELY WIDE TEMPERATURE INTERVAL.

Description

The present invention relates to a damping

plastic material.

  It is known to use plastics

  as a filling for the shock absorbers but the characteristics

  operating statistics of the shock absorbers

  previous picnic vary with temperature.

  The present invention is based on the discovery

  te of the fact that this variation in the operating characteristics is due to the differences in coefficients of

  dilation and contraction between the body of the cushioning-

  plastic filling.

  The subject of the invention is a compressed damper.

  with a plastic body, a piston housed in this body and a plastic filling housed

  in this body, characterized in that said body in ma-

  plastic and said filling of plastic material

  that have coefficients of expansion and con-

  traction that are close enough that the ca-

  damping characteristics of said damper are substantially constant over a wide temperature range.

  The invention therefore makes it possible to achieve a damping

  low cost plastic material which has satisfactory operating characteristics on

  a whole relatively wide temperature range.

  Other features and advantages of the

  vention will be better understood on reading the description

  tion which will follow from an exemplary embodiment and with reference to the accompanying drawings in which, Figure 1 is a partial longitudinal sectional view of a damper using the invention, taken along line I-I of Figure 2;

  Figure 2 is a sectional view taken sensitive-

  ment along line II-II of Figure 1; Figure 3 is a graph showing the

  force as a function of the stroke of the damper piston

  sister, at different temperatures.

  In the preferred embodiment of the invention,

  vention, a shock absorber 10 comprises a body 11 in material

  re plastic which is preferably molded and which has a cylindrical side wall 12, an end wall 13 formed from one material and an end wall 14 which is fitted in position at the end of the body 12 which is remote from the wall end 13 and retained in this body by an annular protuberance 15 which is housed in an annular groove 16. A piston 17 is fixed to the piston rod 19 which is slidably mounted in a bore

  of the end wall 14. A chamber 21 is replaced

  folds of a foam 22 with closed cells which compresses when the piston 17 takes the position shown in broken lines, moving from the right to the

left in figure 1.

  The coefficients of contraction or dilata-

  tion of the plastic material of cylinder 11 and of the material

  plastic which constitutes the foam with iron cells

  mes 2 are close enough that the characteristics

  shock absorber ticks are sensitive-

  constant over a relatively wide range of temperatures. This is shown schematically in FIG. 2, in which the continuous lines 23 and 24 represent the dimension of the cylindrical wall 12 at low temperature and the lines 25 and 26 interrupted

  show body size 12 at elevated temperatures

  vee. The foam 22 accompanies the expansion of the interior wall 23 with the same coefficient as that at which the cylindrical wall 12 expands, thereby maintaining the damping characteristics of the damper at a substantially constant value over a relatively large temperature range. , comparatively, by

  example, at the temperature interval that we meet-

  normally in a shock absorber of motor vehicles

  biles. This is shown in FIG. 3, in which the graph representing the variation of the force as a function of the stroke for the piston of the shock absorber 10 shows the characteristics at ambient temperature, at

  low temperature and high temperature. The low temperature

  the temperature is -40 C, the high temperature is 71 C and the ambient temperature is around 21 C. It is

  easy to realize that for all temperatures

  tures between -40 C and 71 C, the characteristics

  that the shock absorber is between the graphs

  low and high temperature.

  The structure described above constitutes a

  low cost friction type shock absorber in the-

  which the foam rubs against the interior of the body, and in which the energy is absorbed by the compression and by the natural hysteresis of an alveolar foam,

  the shock absorber giving operating characteristics

  substantially uniform over a wide temperature range, thanks to the balance between contractions and thermal expansion of the foam

  of plastic and contractions and dilations-

  thermal conditions of the plastic cylinder.

  The preferred materials which produce the results described above are a material known as "Nylon" (registered trademark) for cylinder 12 and a polyurethane foam with cells

  closed for foam 22. It will be obvious that one can adopt other

  very combinations of plastics, provided that it-

  have coefficients of expansion and contraction

  sufficiently close. It will be obvious that we can

  also use plastic with cells or-

green.

  By way of example only, a version which gave satisfactory practical results had a

  "Nylcn" body containing polyurethane foam

  voles closed. The polyurethane foam had a

  mass in the relaxed state of about 384 to 950 kg / m. All-

  However, when placed in the body, the foam

4 2555689

  polyurethane was compressed to a third of its

  1st relaxed, so that she possessed a volu.iaue coasse

  grip between 1 15.0 and 2 880 kg / m3 when the piston

  was in its position represented in solid lines

  bare, that is to say when the shock absorber was not subjected to an external load. Compression of the foam

  to this extent was necessary to ensure re-

  turn the piston to its position in solid lines from the

  gure 1 when the external force exerted on this piston

  was deleted. It will be obvious that the foam can

  sedate does not import any desired initial density in the relaxed state, and also that it can be compressed to more

  of 2,880 kg / m3, depending on the characteristics that are desired

re for the shock absorber.

  Of course, various modifications may be made by those skilled in the art to the device which

  has just been described only by way of non-binding example

  mitative without departing from the scope of the invention.

Claims (8)

R E V E N D I C A T I 0 N S   1 - Shock absorber (10) comprising a body made of   plastic third (11), a piston (17) housed in this body,   a plastic material (22) contained in said body,   characterized in that said plastic body and said plastic material (22) have coefficients of expansion and contraction which are sufficiently   close so that the damping characteristics of the   said shock absorber are substantially constant over everything   a wide temperature range.   2 - Shock absorber according to claim 1, charac-   terized in that said plastic material (22) is a plastic foam.   3 - Shock absorber according to claim 2, charac-   terized in that said plastic foam is kept under compression while said damper   is not subject to an external load.   4 - Shock absorber according to any one of the re-   vendications 1, 2 and 3, characterized in that said ma-   plastic (22) is a closed cell foam.   5 - Shock absorber according to claim 4, charac-   terized in that said closed-cell foam has a density in the non-relaxed state of between approximately 384 and 960 kg / m3 and that it is compressed in said   body k a density of approximately 1,150 to 2,880 kg / m3 when   that the shock absorber is not subjected to an external load re.   6 - Shock absorber according to claim 4, charac-   terized in that said closed cell foam has   a density greater than 2,880 kg / m3 when the damping   seur is not subjected to an external load.   7 - Shock absorber according to any one of the re-   vendications 1 to 6, characterized in that said body is made of a material known under the name of "Nylon" (registered trademark) and in that said plastic material (22) is a polyurethane foam. 6 2555689   8 - Shock absorber according to any one of the re-   vendications i to 7, characterized in that said wide temperature range is between -40 C and 71 C.