FR2486607A1 - Brake hydraulic fluid cooling system - incorporates heat exchanger and circulating pump with differential piston - Google Patents

Abstract

The hydraulic braking circuit for a motor vehicle comprises a hydraulic emitter, at least one hydraulic receiver, a heat exchanger connected in circuit with the emitter and the receiver, and hydraulic fluid pumping devices separate from the emitter and associated with the heat exchanger. The pumping devices comprise a differential piston floatingly mounted in the hollow body. The piston in the hollow body may be subjected to a control such as a compressed-air cylinder, a connecting rod controlled by the output shaft of an electric motor, a cam shaft or a solenoid. The control is governed by a temp. probe responsive to the temp. of the brake fluid at any point in the circuit.

Description

The present invention relates generally to the circuits of

  hydraulic braking, and aims in particular

  those of these braking circuits which are intended to

  for motor vehicles, and more particularly industrial vehicles, public works machinery by

example.

  As we know, a hydraulic brake system

  ge generally comprises at least one brake receiver, which is capable of controlling a brake, whether it is a

  drum brake, disc brake, or neck brake

  , and a transmitter which, connected by a pipe to said brake receiver, is capable of supplying pressurized fluid thereto under the control of a brake pedal available to the user, and which can for example be pneumo-hydraulic or hydraulic action, In service, the brake fluid present in such a circuit is inevitably subjected to heating, due to the heat given off by the brake or brakes that it controls, and one of the problems to be solved in the realization of this circuit is to pocket an untimely local vaporization of this brake fluid, capable, by the phenomenon known as of "vapor-lock", of harming brutally, and dangerously,

  braking efficiency, by creating, between transmitter and

  sensor, a gap in continuity It was proposed for this purpose in the French patent

  NO 1.273.302, to implement, between transmitter and receiver

  a heat exchanger mounted in diversion by comparison

  port to said receiver and capable of ensuring cooling of the

  brake fluid for each brake application.

  But, in this French patent NO 1,273,302, the exchanger

  of heat used consists of a simple cana-

  finned connection, connected by non-return valves on

the receiver concerned.

  Its effectiveness is found in practice to be extremely

  pick, for the following two reasons.

  First of all, with each braking, only is circu-

  In the heat exchanger, add the quantity of fluid effected

  tively displaced during such braking, which is only

  a few cm3, and which represents only a fraction, of the

  from 1 to 5% /, of the total brake fluid contained in the

brake system concerned.

  In fact, in such a circuit, the amount of brake fluid displaced during braking corresponds exactly-

  ment to that repressed by the brake pedal, which "leaks

  would be "unpleasantly under the foot of the user if it

  knows of a significant amount of fluid.

  In addition, each time braking, apart from that, taking into account

  valve system controlling its connection to the receiver

  braking device concerned, the heat exchanger used only intervenes when the brake is released, when the brake is released.

  the brake pedal by the user, the duration of his

  vention is reduced, linked to the fact that it is only the return delivery of the quantity of brake fluid previously displaced. The present invention generally relates to a provision which, more particularly intended

  hydraulic braking systems for industrial vehicles

  triels and in particular those equipped with brake controls of the

  continuous flow type, pneumo-hydraulic or hydraulic, per-

  avoids the shortcomings outlined below

  above, leading to high cooling efficiency

  sought after, and has other advantages as well.

  More specifically, the present invention relates to a hydraulic braking circuit, in particular for a motor vehicle, and more particularly for an industrial vehicle, of the type comprising, between a transmitter and at

  minus a receiver, a heat exchanger mounted as a bypass

  tion with respect to said receiver, and characterized in

  that audit heat exchanger is associated a means of pumping

  page * According to a first embodiment of the invention, such a pumping means in itself constitutes only a passive element, only intervening during braking, under the hydraulic pressure of the brake fluid; it can indeed be a simple differential piston

  mounted floating in a hollow body.

  But, thanks to such a pumping means, the quantity of brake fluid admitted to pass, on each braking, in the heat exchanger, is advantageously a multiple of the quantity of this brake fluid strictly necessary for controlling the receiver. .

  The cooling of this brake fluid is thereby affected.

  ve advantageously intensified and accelerated, In addition, in addition to the heat exchanger implemented intervenes advantageously, not only during brake release, but also during braking, from the action of the user

  on the brake pedal, its duration of intervention is advanced

  markedly independent of such an action.

  In practice, it can advantageously be extended considerably.

  The desired cooling is still intense.

  sified. Finally, such a pumping means is particularly safe, without the risk of any failure liable to

  disrupt the operation of the assembly.

  According to another embodiment of the invention,

  the pumping means used constitute an active element

  tif, able to intervene at any time, especially between two

  braking, for example under the control of a means of

  control controlled by a temperature sensitive temperature sensor

  braking fluid temperature at any point on the circuit concerned, with the same effects as above

on the desired cooling.

  In all cases, the efficiency of the heat exchanger

  their associated pumping means implemented in the circ-

  hydraulic brake booster according to the invention is confirmed by the observation of great stability in the travel of the transmitter, characteristic of recondensation

  systematic brake fluid vapors in the circuit

  braking cooked, as well as by observing an increase

  important during systematic braking tests

  repetitive, of the time necessary for the appearance of the pheno-

  leads to "vapor-lock", compared to that observed under the same conditions in previous conventional braking circuits. Overall, it can be estimated that the heat exchanger with associated pumping means implemented in the circuit

  braking hydraulics according to the invention allows a re-

  duction of several tens of degrees as well of the

  brake fluid temperature treated as temperature

  ture of the receptors themselves.

  In addition, independently of the cooling of the brake fluid from which it originates, the heat exchanger with associated pumping means implemented in the hydraulic brake circuit according to the invention also has the advantage of improving the conditions. circulation of this

  brake fluid during braking.

  Indeed, each receiver served no longer constituting a cul-de-sac for such a brake fluid, the risks of pelletization of such a receiver by this brake fluid

  are advantageously reduced.

  The characteristics and advantages of the invention remain

  will emerge from the description which follows, in

  reference to the attached schematic drawings in which s

  FIG. 1 is an overall block diagram of a circuit

  hydraulic brake booster according to the invention;

  Figure 2 is, on a larger scale, a side view

  axial pe of the heat exchanger with associated pumping means

  cie that according to the invention comprises this hydraulic circuit

  brake, with a schematic representation of the receivers

  teurs served by it; Figure 3 is a view similar to that of Figure

  2 and illustrates an operating phase of the pumping means

  page shown; Figure 4 is a view similar to that of Figure 1 and relates to an alternative embodiment of the invention;

  Figures 5 to 8 are schematic views related

  each carrying respectively various alternative embodiments of the pumping means to be implemented according to the invention.

  These figures illustrate, by way of example, the applica-

  tion of the invention to a hydraulic braking circuit for a motor vehicle, and more particularly for an industrial vehicle, FIG. 1 is a diagrammatic representation, and

  partially, at 10, one of the axles of such a vehicle

  hicle, and in 11A, llB the brakes associated with the two wheels

or set of wheels thereof.

  It is, in the embodiment shown,

  disc brakes each comprising a disc 12, securely

  re of the corresponding wheel shaft, two brake pads

  ge 13, each arranged respectively on either side of

  this disc 12, and, for the application of these brake pads

  swims 13 to disk 12, a control piece 14, or clamp.

  In such a control piece 14 is included a

  receiver, respectively 15A, 15B, consisting, for example, and as shown, of a cylinder 16 in which is slidably mounted, in the direction of the disc 12, a piston 170 The service of such a receiver 15A, 15B is ensured

  by a transmitter 19, under the control of a control valve

  of 26 actuated by a brake pedal 20 available

  tion of the user; usually, at the transmitter 19 is

associated a tank 38.

  In the embodiment shown, on the cana-

  reading 21 connecting the transmitter 19 to the receivers 15A, 15B

  a corrector 22 is interposed, suitable, for example, for inter-

  come depending on the load to which the

god 10.

  These arrangements are well known in themselves, and not forming part of the present invention, they will not be described in more detail here,

  In a manner also known per se, provision is made,

  be the transmitter 19 and a receiver 15A, 15B, a heat exchanger 23, mounted as a bypass with respect to such a receiver 15A, 15B. In the embodiment shown in FIG.

  1, such a heat exchanger 23 is common to both

  receivers 15A, 15B associated with the axle 10 concerned, In practice, the pipe 21 splits into two branches 21 ′, 21 ", the first connected to the receiver A for example, and the second connected to the heat exchanger 23, Jointly, by a line 24, it

  is connected to the 15B receiver for example, and the receivers

  15A, 15B are connected to each other by a cana-

reading 25.

  In other words, by the pipes 21 ', 21 ", 24 and 25, the heat exchanger 23 and the receivers 15A, 15B are mounted in a loop, said heat exchanger and said 1o receivers being in series within such a loop, and the transmitter 19 being, by line 21, connected in a

point of it.

  According to the invention the heat exchanger 23 is

associated with a pumping means.

  In the embodiment shown in the figures-

  res 1 to 3, this pumping means is incorporated into the heat exchanger 23 and is constituted by a differential piston

  27 mounted floating in the hollow body 28 that comprises it

  this. The floating piston 27 has two ranges, namely

  a span of larger section 29, which axially carries

  te projecting, on its front face, a lug 30, and a span of smaller section 31, Figure 20 In the embodiment shown, the hollow body 28 is formed of a shoemaker 32 and a cover 33 attached to this case 32 for its closure, for example at

using screws (not shown).

  Anyway, the hollow body 28 has two bores, namely a bore of larger section 349 in which the bearing 29 of the floating piston 27 is slidably mounted, and, following the previous one, in the axis of this one, a bore 35, in which es; t sliding mounted

  the range 31 of said floating piston 27.

  In the embodiment shown, the slide-

  ment of the bearing surfaces 29 and 31 of the floating piston 27 in the bores 34 and 35 of the hollow body 28 is sealed, said bearing surfaces 29 and 31 being equipped for this purpose,

  their periphery, seals 36, 37.

  The floating piston 27 delimits three chambers in the hollow body 28, namely a first chamber 39, at the front

  of its range of larger section 29, a second cham-

  bre 40, which is annular, around its more limited range

  tite section 31, and a third bedroom 41, at the back

of it.

  By the branch 21 "of the pipe 21, the chamber 40 of the hollow body 28 is, on the side of the bearing surface of smaller section 31 of the floating piston 27, connected to

the transmitter 19.

  By the pipe 24, the chamber 39 of the hollow body 28 is, on the side of the scope of greatest section 29 of the piston 27, connected to the receiver 15B, and, by the latter and the pipe 25 to the receiver 15k, said receiver 15A being itself connected to the transmitter 19 by the branch 21 'of

line 21.

  So therefore, in the embodiment shown,

  the transmitter 19 is connected to the loop formed by the sample

  heat gor 23 with pumping means according to the invention and the receivers 15A, 15B at a point of this loop located on the side of the range of smallest section 31 of the piston 27

of said pumping means.

  Finally, by a nozzle 43, the chamber 41 of the hollow body 28 is, at the end of the range of smaller section 31 of the

  floating piston 27, connected to the atmosphere.

  In the embodiment shown, the connection to the atmosphere of this chamber 41 is made directly, by

the nozzle 43.

  Alternatively, it can also be done via the

  medium of the reservoir 38 associated with the transmitter 19, a channel

  reading 42 then connecting the nozzle 43 to this tank 38, as shown diagrammatically in broken lines in FIG. 1, This arrangement advantageously ensures a systematic return to such a tank of oil leaks,

  could possibly be the object the hollow body 28.

  Preferably, and as shown, the floating piston

  as long as 27 is, in the hollow body 28, subjected to a biasing spring 45, which urges it permanently towards a rest position, for which, in the embodiment shown in Figures 1 to 3, it is supported by its lug 30 against the cover 33 of this body

  hollow 28, on the side opposite the transmitter 19.

  Preferably also, and as shown, the hollow body 28, which belongs to the heat exchanger 23,

  is externally projecting from cooling fins

  dissement 46, both with regard to its case 32 and with regard to its cover 330 Likewise, and as schematically shown in broken lines in FIG. 19, the pipe 25 connecting the two receivers 15A to each other , 15B can carry

  transversely of the cooling fins 47.

  Such cooling fins can also

  equip, if desired, the other pipes.

  When braking, depressing the pedal 20

  evokes the sending, by the transmitter 19, of a continuous flow of

  pressurized fluid in line 21, as dried

  m.atiéz by the arrow Pl in Figure 20 Let P be the pressure of this pressurized fluid, If the section of the span of larger section 29 of the floating piston 27, and S2 the section of the span of smaller

section 31 of it.

  Let F also be the force exerted by the spring 45

on the floating piston 27.

  By the branch 21 "of the pipe 21, the pressurized fluid exerts its effects, in the chamber 40 of the hollow body 28, on the rear face of the span of greater section 29 of the floating piston 27, Given the continuity of the hydraulic circuit, it also exerts its effects, in the chamber 39 of the body

  hollow 28, on the front face of the span of greater sec-

  tion 29 of the floating piston 27, but over a larger area than the previous one, since it is a piston

differential.

  By construction, by an appropriate choice of sections

  If, S2 of the differential piston 27 and the stiffness of the res-

  exit 45 and taking into account the minimum pressure to be deployed during braking, it is ensured that the force to which the floating piston 27 is subjected, in the chamber 39 of the hollow body 28, is in any event, during such braking, greater than all of the forces to which this floating piston 27 is also subjected in the chamber of said hollow body 28, according to the following inequality:

P.S1> P. (S1-52) + F

  in which, for simplicity, it was not required

account of the performance of the whole.

  During braking, the floating piston 27 therefore leaves its initial rest position, FIG. 2, the spring 45 yielding elastically, and it moves towards a service position, FIG. 3, for which, in the example embodiment shown, it is supported on the bottom of the chamber 41 of the hollow body 28, while the spring 45

is compressed.

  In practice, the speed of movement of the floating piston

  as long as 27 is proportional to the hydraulic brake pressure. Let p be the axial stroke of the floating piston 27 between its rest position and its service position, as indicated in FIG. 3 in which said rest position has been

  shown schematically in broken lines.

  Passing from this rest position to this operating position, the floating piston 27 discharges pressurized fluid which, from the chamber 40 of the hollow body 28 gains the

  room 39 of it, by successively embranche-

  elements 21 ″ and 21 ′ of line 21, along arrow F2 in FIG. 2, receiver 15A, line 25, receiver 15B and line 24, along arrow F3,

of this figure 2.

  Let Vl be the volume of pressurized fluid thus discharged

  when braking by the floating piston 27 when the latter passes from its rest position to its service 355 position, Let V2 be the volume of fluid under pressure then entering the chamber 39 of the hollow body 28, Let V3 finally the volume of fluid under pressure delivered

  by the transmitter 19 during such braking.

  In the exemplary embodiment shown, the volume V2 results from the junction of the volumes Vil and V>:

V2 = VI + V3

  and it is this volume of fluid V2 which is allowed to circulate

in receptors 15A, 15B.

  Now, in practice, the volume of fluid V1 discharged by the floating piston 27 during braking is a multiple of

  volume of fluid V3 then delivered by the transmitter 19.

  The volume of fluid V2 sweeping the receivers 15A, 15B during braking is therefore advantageously itself a multiple of the only volume of fluid V3 delivered by the transmitter 19. The heating of the brake fluid in the receivers 15A, 15B is therefore limited, and this is all the more so since these no longer constitute a dead end, when the brake is released, that is to say when the user releases his action on the pedal 20, the transmitter 19 becomes inactive, and the entire hydraulic circuit supplied by it

  is put at atmospheric pressure.

  Consequently, the floating piston 27 is subjected only to

  effects of spring 45, and this causes the return to po-

  rest position of this floating piston 27.

  During such a return to the rest position, the floating piston 27 discharges, via the pipe 24, along arrow F'3 in FIG. 3, the fluid previously contained in the chamber 39 of the hollow body 28 and a volume V2 of this fluid is admitted again to circulate, but in the opposite direction, in the receivers 15B, 15A, this volume V2 then subdividing, on the one hand, into a volume of fluid V3 which, via the pipe 21, returns to the transmitter 19 along arrow E'l of Figure 3, and on the other hand in a volume of fluid

  Vl which, by the branch 21 "of the pipe 21, re-

  reaches the chamber 40 of the hollow body 28, along the arrow

P'2 of figure 3.

  As will be noted, the fluid then circulating in the receivers 15A, 15B has been previously cooled by its passage through the hollow body 28, the latter constituting it

  the heat exchanger 23 provided for this purpose.

  The return of the floating piston 27 to the rest position is ensured by the biasing spring 45 associated therewith, and, taking account of the preceding conditions, this spring is chosen so that the duration of such a return, including depends on the duration of the brake release intervention

  of the heat exchanger 23, which is largely extended

  beyond such a brake release; this duration can for example

dye 20 to 35 seconds.

  Of course, the return movement of the floating piston 27 towards its rest position can be interrupted if a new pushing action is exerted by the user.

on the brake pedal 20.

  Of course also, with each brake application,

  that is to say at each cycle of depressing and releasing the brake pedal 20 by the user, the operations described

above are repeated.

  In other words, for each brake application, there is sys-

  a double circulation, first in a sense,

  then in the other, fluid in the brake receptors

  ge 15A, 15B, such a fluid being each time cooled by

  its passage through the heat exchanger 23.

  Preferably, the hollow body 28 thereof is made up of

  made of a light and good conductor of heat,

  such as aluminum or an aluminum alloy.

  The transmitter 19, instead of being connected from the side of the range of smaller section 31 of the piston 27 of the means of

  pumping can of course be connected to any other

  be point of the loop formed by the heat exchanger 23

and receptors 15A, 15B.

  It can, for example be connected to the pipe 24, and therefore from the side of the scope of larger section 29

of piston 27.

  However, in this case, the volume of fluid which circulates in the receivers 15A, 15B during braking is formed only from the only volume of fluid V1 discharged by the piston 27, at

  excluding the volume V3 delivered by the transmitter 19.

  While still being a multiple of volume V3, this

  fluid volume is therefore less than the previous one.

  According to the variant of implementation illustrated by the

  Figure 4, there is provided a heat exchanger 23 individual

duel for each brake.

* In the embodiment shown, and for the

  scanning of the receiver concerned by a maximum volume of fluid

  badly during braking, the hollow body 28 of the pumping means

  page implemented according to the invention is preferably connected to the transmitter 19 of the side of the scope of smaller section of the piston 27 which this pumping means comprises and to said receiver on the side of the scope of larger section

  of this piston, as in the form of implementation of the

  vention illustrated by Figures 1 to 3.

  But, as indicated above, a provision

  can also be adopted0 Of course, the pumping means used in

  the heat exchanger according to the invention can be different

  rent from the simple differential piston more particularly

described above.

  In particular, according to a development of the invention, instead of being free, and therefore constituting a passive element intervening in itself only under the hydraulic pressure of the brake fluid, this pumping means can

  be under the control of a control means.

  For example, in Figure 5, the pumping means used

  vre according to the invention can be constituted by a piston

  27, which is analogous to that described above, and which, -

  like him, is mounted mobile in a hollow body 28, but

  which, instead of being a floating piston, is subjected in a way

  re positive to a compressed air cylinder 50, the piston 51

  this jack being coupled by a rod 52 to said piston 27.

  In Figure 5, elements similar to those described

  previously received the same reference; this is how, -

  in particular, that, as before, the piston 27 is subjected

  to a biasing spring 45 which biases it directly

  tion of a rest position, which is that shown. The rod 52 naturally passes through the bottom of the chamber 41 of the hollow body 28, a seal 53 being provided.

2486-607

for this purpose around it.

  On the body 54 of the compressed air cylinder 50 are pre-

  views, on the one hand a pipe 55, on a first side of the piston 51, for supplying compressed air, and on the other hand a pipe 56, on the other side of the piston 51,

for venting.

  In practice, the compressed air supply to the cylinder

  can be done in two different ways.

  For example, it can be done from the command

  of braking itself, through the air valve of this

  control, upstream of the air-brake fluid interface

  respondent; in such a case, the jack 50 plays the role of a means of assistance which adds its effects to that of the hydraulic braking pressure alone, the frequency

  actuating the pumping means according to the invention res-

  both linked, as before, to the number of braking operations carried out

  you are. But as a variant, it can be slaved for example to

  a temperature sensor sensitive to the temperature of the fluid

  of braking at any point on the circuit concerned.

  It therefore intervenes advantageously systematically-

  ment, as soon as the temperature of the brake fluid at the point considered reaches a critical value, and no longer only during braking, including when the vehicle concerned

is at a standstill.

  Such an arrangement, which ensures a self-contained

  me of the piston 27, independently of any braking, allows

  advantageously to eliminate any possibility of "vapor-

  lock "when the brakes served are no longer applied

  or that the vehicle concerned is temporarily immobilized.

  A control of the cylinder 50 by vacuum can also

be considered.

  According to the variant embodiment illustrated in FIG. 6, the control means to which the piston 27 is subjected is a solenoid 58, the rod 52 to which this piston 27 is coupled being integral with the movable core 59 controlled by

this solenoid 58.

  As a variant, FIGS. 7 and 8, it is a motor 14,

  electric 60, or that the rod 52 is coupled by a

  connecting rod 61 to the output shaft of this electric motor, in practice by the intermediary of a reduction gear, either that it is subjected to a cam 62 wedged on such a shaft; in the first case, no bias spring is necessary for the piston 27, and, in the second case, the bias spring

  polarization 45 implemented is arranged so as to hand-

  hold the rod 52 in contact with the cam 62, As before, the solenoid 58 or the motor 60

  constitute control means capable of being ass-

  served to a temperature probe.

  In the foregoing, it has been assumed that the pumping means associated according to the invention with the heat exchanger used was incorporated into said heat exchanger, the hollow body in which the piston of such means is slidably mounted pumping externally carrying fins

  and thus forming by itself a heat exchanger.

  This is not necessarily so

  On the contrary, the pumping means can, according to a

  of embodiment of the invention not shown, form a separate member of the heat exchanger, possibly at a distance therefrom, For example, this pumping means can be integrated with the receiver which it serves, or more precisely with the

  corresponding brake, while the heat exchanger

  which it is associated with is located outside of such a brake, in the very structures of the vehicle concerned. The present invention is moreover not limited to

  embodiments and implementations described and

  presented, but includes any variant.

  In particular, the brakes served may include

  several pistons and / or the same heat exchanger

  vir more than two receivers.

  In addition, the piston which comprises the pumping means

  according to the invention, instead of being rigid, as shown

  felt, can also be made of a rubber membrane, Finally, this piston, instead of sharing in two unequal chambers, for its resting position, the hollow orps in which it is mounted movable, can share it in of them

  substantially equal chambers; for example, when his po-

  rest position is defined by a lug, said lug is sufficiently axially extended for this purpose.

Claims (13)

  1. Hydraulic braking circuit, in particular for a motor vehicle, and more particularly for an industrial vehicle, of the type comprising, between a transmitter and at least one receiver, a heat exchanger mounted bypass with respect to said receiver, characterized in that 'at   said heat exchanger there is associated a pumping means.   2. Hydraulic braking circuit as claimed   cation 1, characterized in that said pumping means is constituted by a differential piston mounted floating in a hollow body *   3. Hydraulic braking circuit as claimed.   cation 1, characterized in that said pumping means is constituted by a piston mounted movably in a hollow body and subjected to a control means such as a compressed air cylinder   crankshaft controlled by the output shaft of a 6lec- engine   stick, camshaft, solenoid or other.   4. Hydraulic braking circuit as claimed   cation 3, characterized in that said control means is   slaved to a temperature sensor sensitive to temperature-   re brake fluid at any point on the circuit,   5. Hydraulic braking circuit according to one   conch of claims 2 to 4, characterized in that the   hollow body of the pumping means is connected to the transmitter of the   c8té of the range of smaller section of the piston than   carries said pumping means and to the receiver of the side of the range of greatest section of said piston,   6. Hydraulic braking circuit as claimed.   cation 5, characterized in that the hollow body of the pumping means is connected to the atmosphere at the end of the span of smaller section of the piston that said pumping means comprise.   7. Hydraulic braking circuit as claimed   cation 6, characterized in that the hollow body of the pumping means is connected to the atmosphere via the   tank usually associated with the transmitter.   8. Hydraulic braking circuit according to one   conch of claims 2 to 7, characterized in that the   piston which comprises the pumping means is subjected to a biasing spring which urges it permanently in direction of a rest position.   9. Hydraulic braking circuit according to one   conch of claims 1 to 8, characterized in that the   pumping means forms a separate member from the heat exchanger   heat, possibly at a distance from it.   10. Hydraulic braking circuit according to one   conch of claims 1 to 8, characterized in that the   pumping means is incorporated into the heat exchanger.   11. Hydraulic braking circuit according to one   conch of claims 1 to 10, characterized in that the   pumping means is integral with the receiver.   12. Hydraulic braking circuit according to one   conch of claims 1 to 11, wherein the transmitter   serves at least two receivers, characterized in that, by pipes, the heat exchanger and the pumping means associated with it are mounted in a loop with the   so-called receivers, and the transmitter is connected at some point conch of such a loop.   13. Hydraulic braking circuit as claimed   cation 12, characterized in that cooling fins   are provided on at least one of the pipes forming said loop.