FR2812352A1 - Band brake control actuator comprises piston, delimiting chamber, with pushrod connected to it, longitudinal column has second piston fixed to it which is surrounded by bell to delimit second chamber surrounded by third chamber - Google Patents

Abstract

The actuator comprises a first piston (7) delimiting a first chamber (10) in a body. A longitudinal pushrod (8) is connected to the piston and a first spring (24) is between the piston and the body. A longitudinal column (11) carried by the body has a second piston (13) fixed to it. A bell (14) has its base passed through by the column and its cylindrical wall surrounds the second piston to delimit a second chamber (19) surrounded by a third chamber (20). A second spring (25) acts between the bell and the second piston. There are means (5) connecting the first and second chambers to a reference pressure. Pressurized fluid is introduced into the third chamber.

Description

1 Control actuator with several effects The present invention relates to a

control cylinder

several effects.

  With a view in particular to actuating a band brake comprising a braking band of a rotary cylinder, in particular in a gearbox, there is known a control cylinder with gradual effects, which comprises a piston installed in a chamber and connected to a pusher opposite which acts! "n pressurized fluid as well as two springs arranged on the side of the pusher, one of which is disposed between the piston and the wall of the chamber and the other is disposed between the piston and the pusher, so that one of the springs is compressed before the other. Such a jack is however limited as to the forces it is

  likely to develop as a function of fluid pressure.

  The present invention aims to provide a control cylinder which, on the contrary, is capable of significantly increasing the force delivered as a function of the pressure of the control fluid. For this, the control cylinder according to the present invention comprises a body in which is delimited a space having a cylindrical wall and first and second end walls, a first piston movable longitudinally in said space and delimiting a first chamber on the side of the first end wall of said body, a pousso --'-: longitudinal connected to said first piston and which extends through the first end wall of said body, and a first elastic means acting in the direction which moves away

  said first piston and the first end wall of said body.

  The jack according to the invention also comprises a longitudinal column carried by the second end wall of said body and projecting into said space, a second piston fixed on said column and the peripheral edge of which extends away from the cylindrical wall of said space, a bell having a base and a cylindrical part, the base of which is crossed by said column and is disposed between said second piston and the second end wall of said body and whose cylindrical wall surrounds said second piston, so as to delimit a second chamber surrounded by a third chamber, and is capable of coming to bear on said first piston leaving a passage, a second elastic means acting in the direction which moves the base of said bell and said second piston, as well as means for connecting said first and second chambers to a reference pressure, and supply means making it possible to introduce a

  fluid under variable pressure in said third chamber.

  According to the invention, said first elastic means is less strong than said second elastic means so that as long as the fluid pressure is less than a value such that said bell is not in contact with the first piston, the force likely to be generated by said pusher depends on the difference between the pressure of the fluid in said third chamber and the pressure in said first chamber and so that when the fluid pressure is greater than a value such that said bell is in contact with the first piston, the force likely to be generated by said pusher depends on the difference between the pressure of the fluid in said third chamber and the pressure in said first chamber and additionally on the difference between the pressure of the fluid in

  said third chamber and the pressure in said second chamber.

  According to an alternative embodiment of the present invention, the end part of said longitudinal column is slidably engaged in a blind longitudinal channel of said pusher which

  communicates by a lateral passage with said first chamber.

  Said longitudinal column preferably has a blind longitudinal channel opening into the channel of said pusher and communicating by a lateral passage with said second chamber so that said first and second chamber communicate

between them.

  According to the invention, a passage is preferably provided between said bell and said first piston when the latter are in abutment

one over the other.

  According to the invention, said body preferably has a

  passage for venting said first chamber.

  1 According to the invention, said first elastic means is

  preferably arranged in said first chamber.

  According to the invention, said second elastic means is

  preferably arranged in said second chamber.

  The present invention will be better understood from the study of a control jack for a band brake, described by way of non-limiting example and illustrated by the drawing in which: - Figure 1 shows a longitudinal section of a control cylinder according to the present invention, in its rest position; - Figure 2 shows the control cylinder of Figure 1, after a first stroke; - and Figure 3 shows the control cylinder of Figure

1 after a second race.

  The control cylinder 1 shown in the figures comprises a body 2, for example a gearbox housing which comprises a cylindrical wall 4, a radial end wall 5 and a

  radial end cover 6, defining a cylindrical space 3.

  In the cylindrical space 4 is disposed a first piston 7 in the form of a disc, movable longitudinally and connected to a rear part 8b of a longitudinal pusher 8 which passes through it. This pusher 8 extends through the end wall 5. A seal 9 is provided between the cylindrical wall 2 and the peripheral face of the piston iA

mobile 7.

  Thus, a first chamber 10 is delimited in space 3, between the end wall 5 and the movable piston 7, and its volume

  varies depending on the longitudinal position of this movable piston.

  The control cylinder i further comprises a longitudinal column 11 whose rear end 11a is fixed, by any known means, to the cover 6 and whose front end part 11b is slidably engaged in a blind longitudinal orifice 12

  formed in the rear part 8b of the pusher 8.

  At a distance on the one hand from the end wall 6 and on the other hand from the piston 7, the longitudinal column 11 fixedly carries a second piston 13 in the form of a disc, the peripheral face of which is at a distance

  1 of the cylindrical wall 4 of the space 3.

  The control cylinder 1 further comprises a bell 14 which comprises a base wall 15 disposed between the end wall 6 and the fixed piston 13 and which is traversed by the column 11. This base wall 15 is fixed on a slide annular 16 movable on the column 11. The bell 14 further comprises a cylindrical portion or skirt 17 which extends longitudemeremer :. so as to surround the piston 13, a seal 18 being disposed between the piston 13 and the face

inside of the skirt 17.

  Thus, the fixed piston 13 and the bell 14 define, inside the latter, a second chamber 19 whose volume varies as a function of the position of this bell relative to this fixed piston. This second chamber 19 is consequently surrounded by a third chamber 20 which generally extends between the end wall 6 and the base 15 of the bell 14, between the skirt 17 and the wall 4 of the casing 2 and between the piston 7 and the piston 13. The front peripheral edge 17a of the skirt 17 is formed so as to leave one or more passages

  on the side of the cylindrical wall 4 of the space 3.

  The column 11 has, in its front part 11 lb, a longitudinal channel 20 which opens into the orifice 12 of the pusher 8 and a radial channel 21a which puts in commu; uation this longitudinal channel 20 and the chamber 19. The pusher 9 has a radial passage 22 for communicating its longitudinal orifice 12 with the first chamber 10 and the end wall 5 has a passage 23 for communicating the chamber 10 with the atmosphere, so that the first chamber 10 and the second chamber 19 are connected to the atmosphere. Helical springs 24 are arranged in the chamber 10, between the end wall 5 and the piston 7, and act in the direction which separates them. Coil springs 25 are arranged in the second chamber 19, between the piston 13 and the base 15 of the bell 14, and

  act in the direction that pushes them aside.

  The springs 24 are constructed so as to develop lower compressive strength forces than those of the

springs 25.

  In addition, the cylindrical wall 4 has, on the side of the end wall 6, a channel 26 for supplying the chamber 20 connected to a source of a pressurized fluid, for example oil not shown. Finally, the front end 8a of the pusher 8 is intended to act on an ear 27 of a braking band 28 which is applied to the

  outer surface of a rotating cylinder 29.

  The control cylinder 1 which has just been described is

  sized and adapted to operate in the following manner.

  In its rest position shown in Figure 1, the cylinder

  1 is in the following state.

  The piston 7 and the pusher 8 as well as the bell 14 are in

remote positions.

  The piston 7 is supported in front of the fixed piston 13 carried by the column 11, the springs 24 being in extension and the front end 8a

  of the pusher 8 being spaced from the ear 27 of the braking band 28.

  The base 15 of the bell 14 bears against the front face of the end wall or cover 6, the springs 25 being in extension and the front peripheral edge 17a of the skirt 17 of the bell 14 being at

distance from the movable piston 7.

  Feeding the chamber 20 via the supply channel 26 with oil under increasing pressure, this pressure acts on the movable piston 7 which moves forward against the springs 24 in

  pushing push button 8 forward.

  The front end 8a of the pusher 8 then reaches the ear 27

  of the brake 28 after having traveled the corresponding stroke.

  As the oil pressure continues to increase in the

  chamber 20, the pusher acts accordingly on the ear 27.

  The pressure of the oil continuing to increase in the chamber 20, the bell 14 moves forward against and compressing the springs 25. An intermediate position is shown

in figure 2.

  When the pressure of the oil in the chamber 20 reaches a sufficient value, the front peripheral edge 17a of the skirt 17 comes to bear on the rear face of the movable piston 7. The rear face of the piston 7 has projecting parts 7a against which the front edge 17a of the bell 14 is supported and so that the oil can pass. This position is shown in FIG. 3. The pressure of the oil cz: continuing to increase, the pressure of the fluid acts on the movable piston 7 and on the bell 14 and the pusher 8 acts on the ear 27 accordingly . The force exerted by the pusher 8 on the ear 27 results from the force generated by the pressure of the fluid exerted on the movable piston 7, to which is added the force

  generated by the pressure of the fluid on the bell 14.

  It follows from the above that, as long as the pressure of the fluid in the chamber 20 is less than a value such that the bell 17 is not in contact with the piston 7, the force generated by the pusher 8 depends solely on the pressure of the fluid in the chamber 20 relative to the atmospheric pressure in the

room 10.

  On the other hand, when the pressure of the fluid in the chamber 20 is greater than a value such that the bell 14 is in contact with the movable piston 7, the force generated by the pusher 8 results, cumulatively, from the difference between the paLssion of the fluid in the chamber and the atmospheric pressure in the chamber 10, which acts on the movable piston 7, and of the difference between the pressure of the fluid in the chamber 20 and the atmospheric pressure of the chamber 19, which acts on

bell 14.

  The present invention is not limited to the example described above. Many variants are possible without departing from the

  framework defined by the appended claims.

Claims (7)

1 CLAIMS   1. Control cylinder, characterized in that it comprises - a body (2) in which is delimited a space having a cylindrical wall and first and second end walls, - a first piston (7) nkbile longitudinally in said space and delimiting a first chamber (10) on the side of the first end wall of said body, - a longitudinal pusher (8) connected to said first piston and which extends through the first end wall of said body, - a first elastic means (24) acting in the direction which separates said first piston and the first end wall from said body, - a longitudinal column (11) carried by the second end wall of said body and projecting into said space , - a second piston (13) fixed on said column and the peripheral edge of which extends away from the cylindrical wall of said space, a bell (14) having a base and a cylindrical part, the base of which is crossed by the adite column and is disposed between said second piston and the second end wall of said body and whose cylindrical wall surrounds said second piston, so as to delimit a second chamber (19) surrounded by a third chamber (20), and is susceptible to come to bear on said first piston leaving a passage, - a second elastic means (25) acting in the direction which moves the base of said bell and said second piston, - means (5) for connecting said first and second chambers at a reference pressure, - supply means (26) making it possible to introduce a fluid under a variable pressure into said third chamber, said first elastic means being less strong than said second elastic means so that as long as the pressure of the fluid is less than a value such that said bell is not in contact with the first piston, the force likely to be generated by said 1 plunger depends on the difference between the pressure of the fluid in said third chamber and the pressure in said first chamber, via said first piston, and such that, when the pressure of the fluid is greater than a value such that said bell is in contact with the first piston, the likely effort generated by said pusher depends on the difference between the pressure of the fluid in said third chamber and the pressure in said first chamber and additionally on the difference between the pressure of the fluid in said third chamber and the pressure in said second bedroom,   via said first piston and said bell.   2. Control cylinder according to claim 1, characterized in that the end part (1 lb) of said longitudinal column (11) is slidably engaged in a blind longitudinal channel (12) of said pusher which communicates by a lateral passage (22) with said first chamber, that said longitudinal column having a blind longitudinal channel (21) opening into the channel of said pusher and which communicates by a lateral passage (21a) with said second chamber so that said first   and second bedroom communicate with each other.   3. Control cylinder s ,,) one of claims 1 and 2,   characterized in that a passage (7a) is formed between said bell   and said first piston when the latter are in contact with one another.   4. Control cylinder according to any one of   previous claims, characterized in that said body   has a passage (22) for venting said first chamber. 5. Control cylinder according to any one of   previous claims, characterized in that said first   elastic means (24) is disposed in said first chamber.   6. Control cylinder according to any one of   previous claims, characterized in that said second   elastic means (25) is disposed in said second chamber.   7. Control cylinder according to any one of   previous claims, characterized in that said pusher (8) acts on a band brake (28).