FR2790294A1 - Break and clutch hydraulic control unit for cars includes inner bore with front and rear parts formed in front and rear parts of cylinder body and seal housed in central component of cylinder body - Google Patents

Abstract

Control unit (10) includes cylinder body (17), piston (42) sliding in inner bore (22) and dynamic seal (59a, 59c) borne by cylinder body. Cylinder body has blind front component (17a) with base (24), central component (17b) and rear component (17c) open rearwards. Inner bore has front (22a) and rear (22c) portions, and dynamic seal is housed in central component of cylinder body.

Description

The invention relates to a hydraulic brake control device or

  a clutch, in particular for a motor vehicle, comprising at least one emitting or receiving cylinder provided with a piston. The invention relates more particularly to a hydraulic brake or clutch control device of a motor vehicle comprising at least one cylinder comprising a cylinder body having at the front a bottom io and open at the rear, a piston sliding axially in an internal bore of the cylinder body, at least one dynamic seal carried by the cylinder body to cooperate with the external periphery of the piston, in which the cylinder body is made of synthetic material such as plastic, and in which the piston has a face

  before delimiting a hydraulic chamber.

  Such a device is described, for example in documents DE-U-295 16,488, FR-B-274920 or in the

  French patent application No. 98.07213 of June 9, 1998.

  The object of the invention is to propose a control device of the type mentioned above, the manufacturing costs of which are reduced by simplifying the design of the body.

cylinder.

  For this purpose, the control device according to the invention is characterized in that the cylinder body comprises, arranged axially consecutively from front to rear, a blind front part comprising said bottom, a central part, and a rear part open towards the rear which are tightly fixed together, in that the internal bore comprises a front portion and a rear portion which are formed in the front part and, respectively, in the rear part of the cylinder body, and in that that said dynamic seal is housed in the central part of the cylinder body. Thanks to such a design, it is in particular possible to standardize the front and rear parts of the cylinder body and to constitute a range of products by producing a range of central parts which differ from each other in particular for incorporating supply means for the hydraulic chamber and means for fixing the control device which vary from one device to another depending on

  io in particular the model and type of vehicle to be fitted.

  According to other characteristics of the invention: - said waterproof fixing is a fixing by gluing - said waterproof fixing is a fixing made by welding with indirect heat input - said waterproof fixing is a fixing made by welding using at least one energy source of the laser type; - Said waterproof fixing is a fixing by welding by infrared radiation, for example of the laser type; said waterproof attachment is an attachment by ultrasonic welding; said sealed attachment is an attachment by friction welding; said waterproof fixing is a fixing by high frequency welding; - Said waterproof attachment is an attachment by induction welding of ferromagnetic seals; - Said waterproof fixing is a fixing by mirror welding; - the piston extends through the central part of the cylinder body with radial clearance - a rear tubular section, respectively front, of axial orientation of the front part, respectively rear, of the cylinder body is welded to a front part, respectively rear, complementary to the central part of the cylinder body; - The outer peripheral surface of said tubular section is fixed in a sealed manner by welding with indirect heat supply to an inner peripheral surface of said complementary part of the central part of the cylinder body; o0 - the internal peripheral surface of said tubular section is fixed in a sealed manner by welding with indirect heat supply to an external peripheral surface of said complementary part of the central part of the cylinder body; - Said tubular section is axially abutted against a radial shoulder of the central part of the cylinder body; - The central part comprises a transverse conduit which opens, in a substantially radial direction, into a central hole, of axial orientation, of the central part opposite the external periphery of the piston; - The central part of the cylinder body is shaped as a transverse plate for fixing the control device; - The device comprises two dynamic front and rear seals which are housed in the central part of the cylinder body; - The front dynamic seal, respectively rear, is arranged in a housing formed in the central part of the cylinder body which is open radially inwardly; - The rear end of the rear part of the cylinder body comprises at least one stop intended to cooperate with a rear end of the piston to limit the axial displacement of the piston towards the rear; - The piston comprises a peripheral piston jacket axially integral with the piston and which slides axially in the internal bore of the cylinder body; the piston liner has at least one hole for communication between the inside and the outside of the piston liner, and the hole is intended to move on either side of a dynamic seal

  0 - the piston jacket is metallic.

  Other characteristics and advantages of the invention

  will appear on reading the detailed description which follows

  for the understanding of which reference will be made to the appended drawings in which: - Figure 1 is a view in longitudinal axial section of a first embodiment of a master cylinder produced in accordance with the teachings of the invention and on which the piston is shown in a retracted position; - Figure 2 is a detail view on a larger scale of the central part of the emitter cylinder of Figure 1 which illustrates the tight fixing of the three parts of the cylinder body; and - Figure 3 is a view similar to that of Figure 2

  which illustrates a second embodiment of the invention.

  In the following description, the elements

  identical, similar or analogous will be designated by

same reference signs.

  The figures show a control cylinder in the form of a transmitter of a

  motor vehicle clutch control.

  Such a device (not shown) comprises a sending cylinder connected by a pipe to a receiving cylinder of

  structure similar to the master cylinder.

  Each receiving or emitting cylinder has a piston movable axially inside a cylinder body

  to delimit a hydraulic chamber of variable volume.

  A connection orifice, to which the pipe is connected,

  opens into the hydraulic chamber.

  The master cylinder has a piston rod connected for example to a clutch pedal on which the driver acts or an actuator the starting of which is

  carried out according to predetermined programs.

  The piston of the emitting cylinder is intended to expel a fluid, such as oil, contained in the hydraulic chamber in the direction of the pipe or pipe which connects the cylinder

transmitter to the receiver cylinder.

  When the clutch is engaged, the volume of the hydraulic chamber of the master cylinder is maximum while the volume of the cylinder control chamber

receiver is minimum.

  During the declutching operation, the volume of the hydraulic chamber of the sending cylinder decreases, while the volume of the control chamber of the receiving cylinder increases. The piston of the receiving cylinder then acts on a rod acting, for example, on the declutching fork actuating the declutching stop, which comprises the friction clutch. As a variant, the piston acts in traction via

  a cable or other means on said fork.

  Each transmitter and receiver cylinder has a

  spring acting between the piston and the bottom of the cylinder body.

  When the driver releases his action on the clutch pedal or when the actuator returns to its initial clutch position, the return spring of the master cylinder relaxes to return the piston to its initial position while the return spring of the cylinder transmitter is compressed by the clutch spring, such as a diaphragm, which thus brings the

  piston of the receiving cylinder to its initial position.

  In the figures, the emitter cylinder 10 is shown in the delivery position and comprises a cylinder body 17 io provided with an inlet orifice 18 closed by a plug 19. It is by means of this inlet orifice that the pipe or pipe (not shown), connecting the receiving cylinder (not shown) to the emitting cylinder 10, opens into the

  hydraulic chamber 20 of the emitting cylinder.

  The chamber 20 is of variable volume and it is delimited by the body 17 and the piston 21 mounted movably

  axially inside the cylinder body 17.

  The cylinder body 17 has a generally tubular shape and, in accordance with the teachings of the invention, it consists of three separate parts produced separately by molding in plastic materials which are arranged axially from front to back, that is to say say from left to right considering the figures and among which there is a front part 17A comprising the orifice 18 and the plug 19 at its front axial end, a central part

  or intermediate 17B and a rear part 17C.

  This cylinder body 17 in three parts 17A, 17B and 17C has an internal bore 22 of generally blind shape and of axis XX, corresponding to the axis of general symmetry of the cylinder body 17, with a bottom 24 at the front. of transverse orientation, into which the inlet orifice 18 belonging to a connector 25 opens allowing the previously mentioned pipe to be connected, for example by pinout, the connector 25 internally having for this purpose passages 26 for the passage of a pin used to connect the pipe to the master cylinder. Alternatively, the connector may be of the screw type. The cylinder body 17 is generally open at the rear, that is to say that its rear part 17C is itself

open to the rear.

  Each of the two axial end pieces, i.e.

  o say the front part 17A and the rear part 17C, is in the general form of a tubular part of generally simple design and easy to produce by molding in

plastic material.

  The internal bore 22 for the sliding guide of the piston 21 comprises, in accordance with the teachings of the invention, a front portion 22A formed in the front part 17A and a rear portion 22C formed in the rear part 17C, the two front portions 22A and rear 22C being aligned

and coaxial.

  The piston 21 is capable of sliding in the cylinder body 17, more precisely in the internal bore 22 of the latter, from back to front starting from the retracted disengagement position shown in FIG. 1 towards an advanced position

clutch (not shown).

  In the retracted disengaged position illustrated in FIG. 1, the hydraulic chamber 20 and the control fluid are pressurized while, in the advanced position, the chamber

  and the control fluid are depressurized.

  A projection 28, of generally frustoconical shape, is produced by molding with the transverse bottom 24 and it extends axially rearward in the bore 22 to constitute a centering device for a return spring 29 which is here a helical spring intervening between the cylinder body 17 and the piston 21, more precisely between the transverse bottom 24

and the front of the piston 21.

  Of course, the orifice 18 crosses the bottom 24 and opens laterally relative to the projection 28 coming from

  material by molding with the bottom 24.

  The body of the piston 21 is a molded plastic part of generally tubular shape and it has, at its front part, a transverse wall 30, the transverse face io front 31 of which axially rearwardly delimits the hydraulic chamber 20 and one face of which rear 32 cooperates with the head

a piston rod 33.

  From its front transverse face 30, the body of the piston 21 is extended axially towards the front by a chimney 34, which has a frustoconical profile on the outside, with a central blind hole 35 of cylindrical shape whose bottom, of axial orientation , is formed by the

front face 31 of wall 30.

  The return helical spring 29 is mounted around the chimney 34, the base of which serves as a centering device for the return spring 29, the rear axial end of which bears on the face.

  front 31 of the transverse wall 30 of the piston 21.

  The spring 29 therefore intervenes axially between the bottom

24 and the front face 31.

  The transverse rear axial end face 36 of the projection 28 can constitute a stop with which the transverse axial end face is capable of cooperating.

before 37 of the chimney 34.

  More specifically, in the advanced position, the piston 21 comes into contact through the front face 37 of the chimney 34 with the face 36 of the projection 28, the cylinder body 17 thus having a stop 28 limiting the axial displacement towards the front of the

piston 21.

  From the transverse wall 30, the tubular body of the plastic piston 21 is extended axially towards the rear by a bush 38 having a bore 39, the front bottom of which is delimited by the rear face 32 of the wall

transverse 30 of the piston 21.

  The bottom 32 of the bore 39 is generally in hemispherical shape for reception of the complementary head 40

  1o formed at the front axial end of the piston rod 33.

  The head 40, and therefore the piston rod 33, is retained axially inside the bore 39, and therefore relative to the piston 21, by an elastically deformable element 26 which does not

  will not be described here in more detail.

  1 5 The rod 33 is thus pivotally mounted in the piston 21,

  and more precisely with respect to the bottom 32 of the socket 38.

  The piston 21 carries at its cylindrical external periphery a static seal 41 for piston sealing which is here an O-ring mounted in an internal radial groove formed in the cylindrical external periphery at the right of the transverse wall 30. Other forms of seals sealing statics are possible. The static seal 41 is provided to cooperate with the cylindrical internal peripheral surface of a jacket

piston 42 which is here metallic.

  The piston liner 42 is a tubular element which

  surrounds the piston 21 which is received inside the jacket 42.

  The piston liner 42 is for example based on annoded aluminum or treated steel. The piston liner 42 extends forward in axial projection relative to the chimney 34 so that, in the advanced position not shown, the chimney 34 is in contact with the projection 28, while the transverse edge of front end 42A is at an axial distance from the transverse bottom 24 opposite. The dimensions of the piston jacket 42 are such that the chimney 34 and the return spring 29 are received radially with clearance inside the piston jacket 42. The piston jacket 42 is in intimate contact at its internal cylindrical periphery with the cylindrical external periphery of the piston 21 and with the external periphery of the seal

static seal 41.

  The piston liner 42 is axially integral with the piston 21 and this on the one hand by a radial clamping effect between the piston 21 and the piston liner 42 with cooperation of the static seal 41. To complete this relative axial immobilization of the piston 21 relative to the 1st piston jacket 42, as well as in rotation, it is proposed here that the piston jacket 42 has, near its rear axial end edge 42C, tabs 44 which are received in engagement in a fixing groove 43 formed radially towards the axis XX in the rear end part

38C of socket 38 of piston 21.

  Other means of axial and rotational connection of the piston 21 to the piston jacket 42 can be envisaged

  without departing from the scope of the invention.

  In all cases, a sub-

  piston 21-piston unit unit 42 forming an axially movable assembly in the internal bore 22 of the cylinder body 17, the piston jacket 42 and the piston 21 being

  concentric and coaxial parts of axis X-X.

  The cylinder body is intended to be fixed on a

  fixed part of the vehicle and therefore belongs to the overall part-

  ment of the emitting cylinder 10, while the piston 21 with its piston rod 33 belongs to the movable part of the emitting cylinder. In accordance with the teachings of the invention, the central part 17B of the cylinder body 17 is produced in the form of an intermediate plate disposed axially between

  the front 17A and rear 17C parts of the body 17.

  The plate 17B extends transversely in a plane

  radial orientation perpendicular to the X-X axis.

  The central part 17B forming a fixing plate is made by molding in plastic material and it can for example comprise fixing ears 46 comprising holes 47 for the passage of fixing members, usually screws, of the cylinder body 17, and therefore from the master cylinder 10, on a fixed part of the vehicle

automobile.

  Also shown in Figure 1 a tube 49 integral

  of the central part 17B of the cylinder body 17.

  The tube 49 makes it possible to connect the inside of the cylinder body 17 to a main make-up reservoir (not shown) which is mounted outside the emitting cylinder 10, the hydraulic chambers of the emitting and receiving cylinders being filled with a fluid. hydraulic such as for example oil. The reservoir is partially filled with hydraulic fluid and it is connected by a pipe, not shown in the figures, to the tube 49, the latter opening into an orifice 50 which, in its transverse front end face 45A, the central part 17B. The orifice 50 is one of the ends of a channel 51, of inclined orientation relative to the axis XX, which crosses the central part 17B from its front transverse face 45A to open out towards the rear and axially towards the inside a cylindrical central hole of axial orientation 53 formed in the massive central part and of generally annular cylindrical shape 54 of the central part 17B which, as will be explained later in detail, is substantially coaxial and concentric with the front portions 22A and rear 22C of the internal bore 22, the internal diameter of the cylindrical hole 53 here being greater than the internal diameter of the bore 22 so that the cylindrical external peripheral surface of the piston liner 42 passes through the hole 53 with

  a radial clearance between these two elements.

  o0 The fixing of the tube 49 to the central part 17B is carried out by fitting its rear end into a complementary housing formed in the front transverse face 45A of the central part 17B, then for example by a

  welding operation with indirect heat input.

  1 5 For this purpose, the tube 49 is of course made of a plastic material compatible with that in which is

  molded the central part 17B of the cylinder body 17.

  Referring to Figures 1 and 2, we will now describe the first embodiment according to the invention of the connection and sealing means between the three parts

  constituting the cylinder body 17.

  According to the first embodiment illustrated in FIGS. 1 and 2, the rear axial end 56A, respectively front 56C, of the front part 17A, respectively of the rear part 17C, is produced in the form of a solid tubular section, the l radial thickness is slightly greater than that of the main tubular part of the front part 17A, respectively of the rear part 17C, the two tubular sections 56A and 56C preferably having the same radial dimensions, that is to say in particular the same

  exterior and interior diameters.

  Each tubular section 56A, 56C is received axially in a complementary housing formed opposite in the

center piece 17B.

  More specifically, the massive central part 54 of the central piece 17B in the form of a plate comprises two bushings or ferrules front 27A and rear 27C which extend axially forwards and backwards respectively from the opposite transverse faces before 45A and rear 45C from

the central part 17B.

  o0 Each ferrule 27A, 27C is of generally cylindrical annular shape and produced integrally by molding with the solid central part 54 of the central part 17B and it delimits an internal cylindrical peripheral surface 23A, 23C which opens axially towards the front, respectively towards

  the rear, which is delimited axially towards the rear, respectively

  forwardly, by a transverse front shoulder 64A, respectively rear 64C, each of which constitutes an axial stop which determines the relative axial position of the front part 17A, respectively rear 17C, relative to the central part 17B by virtue of the coming in abutment against this shoulder 64A, 64C of the transverse rear end face 156A, respectively before 156C, of the rear tubular section 56A,

respectively before 56C.

  The cylindrical housings 23A and 23C thus precisely determine the relative axial position of the front parts

  17A and rear 17C of the cylinder body 17 as well as the

  perfect coaxiality of the front 22A and rear 22C portions of the internal bore 22 of the cylinder body 17 in

  which is slidably mounted the piston liner 42.

  Each tubular section 56A, 56C is fitted axially into the corresponding socket 27A, 27C until the faces 156A, 156C come into axial abutment with the

shoulders 64A and 64C.

  The sealed attachment of the front 17A and rear 17C parts to the central part 17B is, in accordance with the teachings of the invention, obtained by means of a welding operation, with indirect heat input, of the sections

  tubular 56A, 56C in the housings 23A, 23C.

  Thanks to the design according to the invention, the sealed welding area 58A, 58C corresponds to the interface between the 1o external peripheral cylindrical surfaces of the tubular sections 56A, 56C and the peripheral cylindrical surfaces

  internal 23A, 23C of sockets 27A, 27C.

  The welding area 58A, 58C in which the welding operation with indirect heat is carried out is thus very precise and limited without the welding operation having any harmful impact on the other parts and the like.

transmitter components 10.

  The design according to the embodiment illustrated in FIGS. 1 and 2 is more particularly adapted to the production of an assembly and of a tight fixing by an operation

  welding by infrared radiation.

  To this end, the central piece 17B according to the invention is produced by molding in a plastic material transparent to infrared rays, while the front end pieces 17A and rear 17C are preferably made from a plastic material which absorbs infrared rays , for example a transparent plastic material identical to part 17B and which is provided with at least one additive such as carbon with a content of 1 to 2% to make it absorbent to said

infrared rays.

  Alternatively, and using two-component molding processes, only the parts intended to be welded together are made from the materials

  transparent or absorbing infrared rays.

  The operation of welding by infrared radiation is then for example carried out by means of a laser beam which causes the welding of the interface zones 58A, 58C. The invention is not limited to the welding operation

  waterproof by infrared radiation.

  It is also possible to make this waterproof fixing by ultrasonic welding, by high frequency io welding or by induction of ferromagnetic seals, these can in particular be produced by introducing small particles.

  ferromagnetic directly in the parts to be welded.

  Alternatively, the fixing is carried out by mirror welding, that is to say using a heating intermediate piece.

that we remove afterwards.

  The sealing of the hydraulic chamber 20 with respect to the outside is here ensured by two dynamic sealing joints front 59A and rear 59C which, in accordance with a characteristic of the invention, are carried by the central part 17B of the body of cylinder 17 and which each cooperate with the external periphery of the piston jacket 42, that is to say with the external cylindrical surface of this piston jacket 42. Each dynamic front seal 59A and rear 59C is here a sealing lip cup which is mounted in a complementary housing 123A, 123C formed in the solid central part 54 of the central part 17B and which is open radially inwards so that each dynamic seal 59A, 59C can cooperate by its radially inner lip with the outer cylindrical surface of the piston liner 42. Alternatively, each seal

  dynamic can be a composite seal.

  The central part 17B thus acts, by its massive central part 54, as a joint box which here carries two dynamic seals, a single dynamic seal

  may be provided without departing from the scope of the invention.

  The housing 123A is open axially towards the front so that the dynamic front seal 59A is axially opposite the rear transverse face 156A of the

tubular section 56A.

  The piston liner 42 has at least one hole 62 io to ensure communication between the interior and the exterior

of the piston liner 42.

  The hole 62 is implanted as a function of the axial movement of the piston 21 with its piston jacket 42 on either side of the lip of the dynamic front seal 59A. When the clutch is engaged, the hole 62 provides communication between the hydraulic control chamber 20 and the external main tank. During the operation of the clutch, the communication is interrupted because the hole 62 is moved by

  with respect to seal 59A, towards the front when considering figure 2.

  Of course, several holes 62 can be provided in the same transverse plane to ensure a greater passage of fluid and avoid having to resort to an orientation

  angular during assembly, the holes 62 being distributed angularly

regularly.

  The communication between the hydraulic chamber 20 and the reservoir takes place through the holes 62 and the axial annular space delimited between the external cylindrical surface of the piston liner 42 and the internal cylindrical surface of the hole

  53 of the massive central part 54 of the central part 17B.

  According to an aspect not shown in the figures, and in order to prevent fluid from escaping towards the outside, there may be provided a sealing bellows intervening between the cylinder body 17 and the piston rod 33, by example between room

central 17B and the piston rod.

  The presence of two dynamic seals 59A, 59C can however make it possible to avoid having to use an additional sealing bellows. In this case, it can be provided, if necessary, an additional cover (not shown) for protecting the rear part 17C which is for example fixed around the rear bushing 27C of the central part 17B and which surrounds the rear part

  îo 17C and is crossed by the piston rod 33.

  Of course, such a protective cover can surround

a sealing bellows.

  The second embodiment illustrated in detail in FIG. 3 differs from the previous one by the arrangement of the tubular sections and the complementary sockets so as to provide an embodiment more particularly suited to a sealed fixing operation by friction welding. For this purpose, the front 27A and rear 27C sockets are received axially inside complementary parts of the tubular sections 56A, 56C which are arranged radially outside the sockets 27A, 27C, that is to say that each of the two sealed welding zones 58A, 58C corresponds to the interface zone between the external cylindrical surfaces of the sockets 27A, 27C and the internal cylindrical surfaces complementary to the radially external parts of the

  tubular sections 56A, 56C formed for this purpose.

  Sealed welding is here preferably carried out by friction at the level of zones 58A and 58C. Welding is performed externally with respect to sockets 27A, 27C by relative vibration and rotation of the front parts 17A and rear

  17C with respect to the central part 17B.

  As a variant not shown, and without departing from the scope of the invention, one of the axial end pieces 17A or 17C can be designed according to the first embodiment, while the other axial end piece 17C or 17A is designed according to the second embodiment. The two axial end pieces 17A, 17C can be produced by molding in the same plastic material or in a different plastic material, and this in particular as a function of the sealed welding technique used for the connection of each axial end piece. piece

central 17B.

  Without departing from the scope of the invention, it is also possible to design the three parts with a mechanical reversal, that is to say that the central part 17B comprises tubular sections extending axially outward which are received in complementary sockets belonging to both

  axial end pieces 17A and 17C.

  Alternatively, the fixing is carried out by gluing. Of course, one of the parts 17A, 17C can be fixed by gluing to the central part 17B and the other of the parts 17A, 17C can be fixed by welding to the part 17B. Thanks to the invention, it is possible, for example, to fix the parts 17A, 17B in one place of manufacture and then finally fix the piece 17C in another place of manufacture. In all cases the central part constitutes a seal holder (s). Of course the presence of the spring 29 is not essential, the return being provided by a spring associated with the brake or clutch pedal. The piston can only be made of plastic and be metallized

  thanks to a surface treatment for contact with the joints.

  By friction welding means for example vibration welding, rotation or mirror. Advantageously, the parts 17A, 17B are force-fitted into the part 17C to allow optimal welding or bonding. Of course one can proceed with a conical fitting. During welding heat can be applied directly to at least one of the parts to be welded. 5

Claims (22)

  1. Device (10) for hydraulic braking or clutch control, in particular for a motor vehicle, comprising at least one cylinder comprising a cylinder body (17) having a bottom (24) at the front and open to the rear, a piston (21, 42) sliding axially in an internal bore (22) of the cylinder body (17), at least one dynamic seal (59A, 59C) carried by the body of the cylinder (17, 17B ) to cooperate with the outer periphery (42) of the piston (21), in which the cylinder body (17) is made of synthetic material such as plastic, and in which the piston (21) has a front face (31 ) delimiting a hydraulic chamber (20), characterized in that the cylinder body (17) comprises, arranged axially consecutively from front to rear, a blind front part (17A) comprising said bottom (24), a central part (17B ), and a rear part (17C) open towards the rear which are fixed together sealed, in that the internal bore (22) comprises a front portion (22A) and a rear portion (22C) which are formed in the front part (17A) and, respectively, in the rear part (17C) of the body cylinder (17), and in that said dynamic seal (59A, 59C) is housed in the central part (17B) of the body of cylinder (17).   2. Control device according to claim 1, characterized in that said waterproof fixing is produced by gluing. 3. Control device according to claim 1 or 2, characterized in that said fixing is carried out by   welding with indirect heat input.   4. Control device according to claim 1 or 3, characterized in that the sealed fixing is a fixing by mirror welding.   5. Control device according to claim 1 or 3, characterized in that said sealed fixing (58A, 58C) is a fixing by welding by infrared radiation, by example of the laser type.   6. Control device according to claim 1 or 3, characterized in that said sealed fixing (58A, 58C)   is a fixation by ultrasonic welding.   7. Control device according to claim 1 or 3, characterized in that said sealed fixing (58A, 58C)   is a fixing by friction welding.   8. Control device according to claim 1 or 3, characterized in that said sealed fixing (58A, 58C)   is a fastening by high frequency welding.   9. Control device according to claim 1 or 3, characterized in that said sealed fixing (58A, 58C) is a fixing by induction welding of seals ferromagnetic.   10. Control device according to any one of   previous claims, characterized in that the piston   (21, 42) extends through the central part (17B) of the body of cylinder (17) with radial clearance.   11. Control device according to any one of   previous claims, characterized in that a section   rear tubular (56A), respectively front (56C), of axial orientation of the front part (17A), respectively rear (17C), of the cylinder body (17) is welded to a front part (27A), respectively rear, complementary to the   central part (17B) of the cylinder body (17).   12. Control device according to any one of   claims 3 to 9, characterized in that the surface   external peripheral of said tubular section (56A, 56C) is fixed in a sealed manner by welding with indirect supply of heat to an internal peripheral surface (23A, 23C) of said complementary part (27A, 27C) of the central part (17B) of the cylinder body (17).   13. Control device according to any one of   claims 3 to 9, characterized in that the surface   ] o internal peripheral of said tubular section (56A, 56C) is fixed in a sealed manner by welding with indirect heat input to an external peripheral surface of said complementary part (27A, 27C) of the central part (17B) of the body cylinder (17).   14. Control device according to any one of   Claims 8 to 13, characterized in that said section   tubular (56A, 56C) is axially abutted against a radial shoulder (64A, 64C) of the central part (17B) of the cylinder body (17).   15. Control device according to any one of   previous claims, characterized in that the part   central (17B) comprises a transverse duct (51) which opens, in a substantially radial direction, into a central hole (53), of axial orientation, of the central part (17B, 54) opposite the external periphery (42 ) of the piston (21). 16. Control device according to any one of   previous claims, characterized in that the part   central (17B) of the cylinder body (17) is shaped as a transverse plate for fixing the control device (10). 17. Control device according to any one of   previous claims, characterized in that it comprises   two dynamic front and rear seals (59A, 59C) which are housed in the central part (17B) of the cylinder body. 18. Control device according to the preceding claim, characterized in that the dynamic front seal (59A), respectively rear seal (59C), is disposed in a housing (123A, 123B) formed in the central part (17B) of the cylinder body which is open radially towards the inside.   19. Control device according to any one of   previous claims, characterized in that the end   rear of the rear part (17C) of the cylinder body comprises at least one stop intended to cooperate with a rear end of the piston to limit the axial displacement of the piston (21, 42) backwards.   20. Control device according to any one of   previous claims, characterized in that the piston   (21) comprises a peripheral piston jacket (42) axially integral with the piston and which slides axially in   the internal bore (22, 22A, 22C) of the cylinder body (17).   21. Control device according to the preceding claim, characterized in that the piston jacket (42) has at least one hole (62) for ensuring communication between the inside and the outside of the piston jacket (42), and in that the hole (62) is intended to move   on either side of a dynamic seal (59A).   22. Control device according to one of   claims 20 or 21, characterized in that the jacket piston (42) is metallic.