FR2504877A1 - MASTER CYLINDER FOR HYDRAULIC BRAKES OF A MOTOR VEHICLE - Google Patents

Abstract

THE INVENTION RELATES TO A MASTER CYLINDER FOR AUTOMOTIVE VEHICLE HYDRAULIC BRAKES. THE MASTER CYLINDER INCLUDES A BODY 1 HAVING A BORE 2 IN WHICH A MASTER CYLINDER PISTON 3 SLIDES WITH A CENTRAL COMPENSATION HOLE 18 CONNECTED TO THE FLUID TANK BY TRANSFER CHANNELS 5 AND AN INTERMEDIATE PISTON 4. THESE TWO PISTONS ARE PUSHED UP BY A SPRING 9, THROUGH THE TWO PLATES 10, UNTIL EACH OF THE HEADS OF THE TENSION ROD 11 BUT against THESE PLATES. THE FIRST TENSION HEAD 13 INCLUDES A PART CONSTITUTING A VALVE BODY 14 RELEASING THE ORIFICE OF THE CENTRAL FLUID COMPENSATION HOLE AT THE TIME OF RELEASE OF THE BRAKE PEDAL. THE INVENTION APPLIES TO MASTER CYLINDERS FOR AUTOMOTIVE VEHICLE HYDRAULIC BRAKES.

Description

The invention relates to a master cylinder for hydraulic brakes

  motor vehicle, comprising at least one master piston

  cylinder, a return spring held captive by means of a central tie rod, and a valve body which is movable relative to the piston and which, when the return spring is relieved, releases an opening of

  compensation on said piston.

  In hydraulic brakes for motor vehicles, it must be ensured that the quantity of liquid in the pressure chamber of the master cylinder and in the entire braking system is automatically supplemented by transfer from a reservoir, in case For this, it is known to generally provide, in the wall of the cylinder, immediately before the piston occupying its rest position, a compensating hole through which the pressure chamber of the master cylinder communicates with the reservoir when the condition The appropriate amount of brake fluid is thus ensured. In addition, pressure compensation between the braking system and the reservoir can take place, for example when the liquid in the brake system expands by heating. actuation of the piston, the latter closes the compensation hole at the beginning of its stroke, so that the rise in pressure required for r braking can take place in the brake system. The mouth of the compensation hole in the interior of the cylinder constitutes a discontinuity of the smooth surface of the bore of the cylinder, against which the piston sealing member must move during each maneuver of the master cylinder. at

  a solicitation of the sealing member of the piston.

  In order to avoid a discontinuity of the surface of the cylinder swept by the piston sealing member, it has already been sought to replace the compensation hole arranged in the wall of the cylinder by a compensating opening on the piston, this opening being

  closed by a valve body when actuating the piston.

  In such a known construction (French Patent No. 1,571,663), the main piston comprises a central compensating hole. The valve body closing this compensation hole is arranged at the front end of an actuating rod of the piston. which can be slightly displaced axially relative to the piston This small inevitable displacement travel constitutes an undesirable clearance when the brakes are actuated. The return spring necessary to return the piston does not attack the piston but the actuating rod of the piston.

  It follows that it is not guaranteed that the compensating hole

  will be released in time when the piston is relieved and there is a risk that at least a brief

  braking system, which can lead to the entry of air into the master-

cylinder -

  In another known construction (German Patent No. 819354), the piston is provided with a head carrying the sealing member of the piston and movable axially relative to the piston, this head releasing, when displaced, the radial channels. arranged in a central bore of the piston, opening frontally, these radial channels constituting the compensating opening As with the construction mentioned above, the structure of the piston and its components is relatively complicated It is the rear face of the organ piston seal which serves to seal the compensating orifice,

  so that this organ is particularly sought.

  With this known master cylinder, there is the particular risk that, in the case where the brake system is force-fed by the rapid and repeated actuation of the piston, the fluid flowing back when the piston reaches its extreme position is still under such a high pressure that the friction of the piston sealing member is not sufficient to open the compensation valve in the piston.

  then a complete release of the brakes.

  In a master cylinder of the kind mentioned at the beginning (German Patent No. 1,243,539), the valve body is constituted by an O-ring which is arranged between a piston-side bearing plate of the piston return spring and a ring which, in the opposite direction, is supported by a compression spring against the piston In the absence of a load, the compensating opening is then between the O-ring and a conical outer surface located on the front end of the piston In this case too, the structure of the

  piston with the valve device to close the compensating opening

  The o-ring must assume a dual function of sealing the piston and the valve body. The piston and the parts that surround it can not be preassembled, but must be introduced successively into the master cylinder.

  so that the editing is relatively complicated.

  From this state of the art, the object of the invention is to provide a master cylinder of the type mentioned at the beginning, but which, while having a configuration relatively simple from the point of view of construction, will allow a pre-assembly of its components. and will guarantee, independently of friction conditions occurring during operation, a reliable opening of the closed compensation orifice

by the valve body.

  According to the invention, this is achieved by the fact that the tie rod for the return spring carries, at its end facing the piston, the valve body which, in the rest position, is at a short distance in front of the opening compensation device arranged in the form of a compensation hole in the front wall of the piston, and in that, in the rest position of the piston, the tie rod pulls the valve body to its open position and constitutes a stop for this body

valve.

  The master cylinder piston is an exceptional achievement

  It has only simple seating surfaces and easy-to-machine holes. Since the compensation hole can be very small and can have, for example, a diameter of 0.5 to 0.8 mm, it follows that the hydraulic force active in the closing direction of the valve is so small that in the release position of the master cylinder it can surely be overcome by the piston return spring,

  so that a reliable opening of the compensation hole is guaranteed.

  Regardless of the type of brake actuation, and the rise in pressure in the brake system, it is ensured that the valve body will clear the compensating opening against the force of the hydraulic pressure, since the tie will transmit at the valve body the force of the piston return spring, or the holding force, opposite the hydraulic pressure, coming from a stop on the

  crankcase or the intermediate piston of a master cylinder.

  In a development of the invention, it is provided that a valve closing spring, biasing the tie rod, is a compression spring arranged between the valve body and a support plate

  the piston return spring, located on the piston side.

  As the relative movement of the valve body is only very small, a very small compression spring with a small deflection can be provided at this point. However, instead of this, it is possible that the closing spring valve is arranged as a compression spring between the end of the tie rod remote from the valve body and the plate associated therewith and serving

  to support the return spring of the piston, or the bottom of the cylinder.

  This solution is preferred if there is very little room for a compression spring in the region between the valve body

  and the spring support plate c 8 piston.

  The valve body is expediently guided in a central hole which frontally comprises the piston, this guidance leaving

  channels of passage are thus obtained in particular.

  Simply a centering of the valve body in the piston.

  In another development of the invention, it is provided that the means for holding each return spring captive are fixed, by their end remote from the valve body, respectively to the bottom of the cylinder and to the intermediate piston This then allows to give to the effective surface of the compensating valve a dimension such that the inner edge of the seal can at the same time serve as a sealing member for the compensating valve An advantage of the large area compensating valves is furthermore that they may have only a very short axial operating stroke, so that the stroke occurring during the actuation of the

master cylinder is tiny.

  The invention will be better understood and other features

  will appear with the following description and accompanying drawings

  o: Figure I shows in longitudinal section a master cylinder in

  tandem for hydraulically actuated motor vehicle brakes

  cally; Figure 2 is an enlarged partial view showing, also in longitudinal section, the master cylinder piston according to Figure 1, with its return spring and the closing means of the compensation hole; Figure 3 shows a longitudinal section of another embodiment of a tandem master cylinder; and FIG. 4 shows, also in longitudinal section, a variant

  embodiment of a master cylinder in tandem.

  The tandem master cylinder shown in FIG. 1 comprises a body or casing I in the bore of which are guided, with

  sealing and sliding possibility, a master piston

  3 and an intermediate piston 4 transfer channels 5 from a reservoir which is only sketched in Figure I open one in the chamber located behind the piston 3, the other in the chamber located behind the intermediate piston 4 Although not shown in FIG. 1, the chamber located behind the piston 3

  is also mounted tight to the right As the intermediate piston

  Diaire 4, as well as the parts which are related thereto, is of identical design to that of the piston 3, only the latter will be described below. The master cylinder piston 3 carries, as a sealing means,

  a primary flexible lip seal 6, which surrounds a cylindrical portion

  drique 7 of the piston 3 which protrudes frontally On this portion 7, bears a plate 8 of support of a spring 9 of the piston, this spring

  being a compression spring which, at its other end, is also

  The restoring spring 9 is held prisoner by a link established by a rod-shaped tie rod or central pull element which traverses axially, with the possibility of movement, the plates 8 and 10 of FIG. spring support

  against each of which it is applied by a head 12, 13.

  The first head 13 of the tie rod 11 is connected to a valve body 14, which engages in a central and frontal bore 15 of the piston 3, bore in which it slides while leaving

  lateral passage channels 16 The valve body 14 is axially located

  forwardly and at a short distance from a central compensation hole 18 arranged in the piston 3, this hole 18 communicating, via a lateral hole 19, with the chamber situated behind this piston 3, and consequently with the transfer hole 5 The outer diameter of the sealing member 17 which ends flush with the front face of the

  valve body 14 is greater than the diameter of the compensation hole 18.

  A compression spring 20 serving as a valve closing spring is arranged between the valve body 14 and the plate 8

spring support, piston side.

  In the drawing, the master cylinder piston 3 is shown in its rest position. If an actuating force acting from the right moves the piston in the bore 2, to the left, the support plate 10 of the spring of return 9 of the piston then bears against the rear side of the intermediate piston 4 Correspondingly, another return spring of the intermediate piston 4 bears against

  the end of the bore of the casing I of the cylinder.

  There is then initially a certain compression of the return spring 9 The pulling It is then released axially, with the same magnitude, so that the closing spring 20 moves the valve body 14 relative to the piston 3, until this body 14 closes the compensation hole 18 From this point begins, in a known manner, the rise in pressure in the pressure chamber located between the piston 3 and the intermediate piston 4 This pressure is transmitted to one of the two brake circuits, while the pressure established in front of the intermediate piston 4 is transmitted to the second circuit of

brakes.

  When the piston 3 returns to its initial position, the valve body 14 is detached from the compensation hole 18 as soon as the return spring 9 is relieved, that is to say as soon as the tie rod serving to imprisonment of the spring 9 transmits, between the two plates 8 and 10, a tensile force which is greater than the force of the spring 20

closing the valve.

  The embodiment shown in FIG. 3, taking as an example the intermediate piston 4 on the left of this figure, resembles the embodiment according to FIG. 2, with the difference that the valve closing spring is arranged between the head 12 of the tie rod 11 away from the intermediate piston 4

and the bottom 2a of the cylinder.

  As in the examples according to FIGS. 1 and 2, the front wall which, opposite the valve body 14, comprises the intermediate piston 4, or the piston 3 in FIGS. 1 and 2, presents

  an obtuse cone 21 in the tip of which opens the compensating hole

18.

  In the case of the master cylinder piston 3 according to FIGS. 3 and 4, and in the case of the intermediate piston 4 according to FIG. 4, the valve body 14 consists of a cylindrical portion 14a which is guided with a leaktight sliding in the central bore 15 of the piston, and by an enlarged plate 14b against which the plate 8 bears. A transverse pin 22 stops the cylindrical portion 14a in the

piston 3 of the master cylinder.

  In the example according to FIG. 3, there is, between the cylindrical portion 14a and a blind bore 23 in the piston 3, a compression spring 24 which, in the rest condition, presses the valve body 14 to its seat. opening position In the realization according to the

2504877.

  4, the same purpose is achieved with a compression spring 25, which bears, on one side, in the vicinity of a sealing member 26 sealing the rod 3a of the piston 3 in the housing 1 and, on the other side, against the pedal end 8a of the rod 3a of the piston 3, and thus moves the piston 3 to its initial position, to the right on

  FIG. 4 Like the head 12 of the tie rod It is held in a position

  wise 27 at the pedal end end of the intermediate piston 4, and as this head is at the same time the counter-support of the spring of

  reminder 9 of the piston 3, and further as the deflection of the piston

  4 is limited to the right by a stop screw 28 screwed into the housing 1, it follows that the spring 25 still pushes the piston 3 to the right when the return spring 9 has already reached its extreme position. determined by the tie rod 11, because of the connection maintaining it captive It follows that the end, c 8 closed cylinder, of the lateral passage channel 16 formed in the form of a longitudinal groove formed on the cylindrical portion 14 a shutter 14, is released so as to overflow frontally beyond

  of the central bore 15 of the piston 3 and that the valve is open.

  In the embodiment of the master cylinder piston according to FIG. 3, the longitudinal groove constituting the passage channel 16 is uninterrupted on the cylinder side. In the closed position, the plate 14b applies sealingly, by its end face, against the primary flexible seal 6 of the piston 3 The closing force acting on this relatively large closure surface of the valve is

surmounted by spring 24.

  The valve arranged frontally on the intermediate piston 4 may be executed according to the example of the piston 3 according to FIG.

figure 4.

  The tandem master cylinder embodiments shown have in common that the return spring 9 of the piston 3, held captive between the latter and the intermediate piston, is prestressed.

  more strongly than is the return spring of the intermediate piston.

  4, arranged between the latter and the bottom 2 of the cylinder, the prestressing supplement corresponding to the force used to move

the intermediate piston 4.

  In the embodiment according to FIG. 4, the part constituting the support plate 10, this part comprising at the same time the hole 27 for the head 12 of the tie rod 11, is anchored by a pin 10a in a bottom hole 2a of the Thus, the force exerted by the spring 25 can be transmitted by the piston 3, the tie rod 11, the intermediate piston 4, the other pulling 11 and the support plate 10 under the effect of the traction force which then appears between the intermediate piston 4 and the valve body 14 associated therewith, the valve arranged in the piston

  intermediate 4 is also open Only when the piston

  medial 4 bears against the screw 28 that the force of the spring 25

  only acts on the valve in the piston 3.

  On the contrary, in the embodiment according to FIG. 3, the force required to open the valves is not transmitted by the casing 1 The spring 24 opens only the valve in the piston 3 For the valve in the intermediate piston 4 , there is no need for any particular opening spring because the closing surface of this valve, determined by the section of the compensation hole 18, is so small that the force of the return spring 9 is sufficient for the opening This combination of the two types of valve shown in Figure 3 allows the two pistons 3 and 4 to be preassembled as a module and to give up a particular attachment against the bottom 2 has the cylinder, while such fixation is necessary in the

embodiment according to Figure 4.

  In the valve embodiments according to the right half of FIG. 3 and according to FIG. 4, the means 10, 11 for establishing a bond of imprisonment are respectively fixed to the bottom 2 of the cylinder and to the intermediate piston 4. examples of embodiment, the cross section of the compensation valve is of a value such that the force of the compression springs 25, 24, which must also be

  as low as possible so as not to compromise the effectiveness of the master-

  cylinder, is insufficient to overcome the force due to the hydraulic pressure in operating condition, while allowing to reliably open the compensation valve The fixing means 10, II at the bottom 2 of the cylinder and the intermediate piston 4 has the effect that the

  valve body 14 is held against the force of the hydraulic pressure.

  while the hydraulic pressure acting on the annular frontal surface of the piston 3, which carries the head 13 of the body of

  valve 14, continues to move this piston in the corresponding direction.

  laying on the release of the brakes, until the

  The compression springs 24, 25 have the task of keeping the pistons in their open position or to bring them to this open position if the hydraulic pressure in the chambers of the cylinder has already disappeared before opening. the compensation valve. Of course, the described embodiments are in no way limitative of the invention. 2504877 i

Claims (8)

  1 Master cylinder for hydraulic vehicle brakes   mobile, comprising at least one master cylinder piston, a return spring held captive by means of a central tie rod, and a valve body which is movable relative to the piston and which, when the return spring is relieved, releases a compensating opening on said piston, said master cylinder being characterized in that the tie rod (11) for the return spring (9) bears, at its end facing the master cylinder piston (3), the valve body (14) which, in the rest position, is at a short distance in front of   compensating opening in the form of a compensating hole   (18) in the front wall of the piston, and in that, in the rest position of the piston (3), the tie rod (11) pulls the valve body (14) to its open position and constitutes a stop for this valve body (14).   2 master cylinder according to claim 1, characterized in that the tie rod (11) is urged by the force of a spring (20) for closing the valve, this force being directed against the hole of compensation (5).   3 drum machine according to claim 2, characterized in that the closing spring (20) of the valve is a compression spring arranged between the valve body (14) and a bearing plate (8) of the return spring (9), this support plate being located c 8 th piston.   4 master cylinder according to claim 1, characterized in that the spring (20) closing the valve is a compression spring arranged between the end of the tie rod (11) away from the body   valve (14) and the bottom (2 a) of the cylinder, or the internal piston mediator (4).   Master cylinder according to claim 1, characterized in that the valve body (14) is guided in the central bore (15) which the piston (3) has frontally, with a clearance for passage (16).   Master cylinder according to Claim 5, characterized in that the valve body (14), guided in the central bore (15) which the piston (3) has frontally, has at least one lateral channel   passageway (16) in the form of a longitudinal groove. 2504877 A   7 Master cylinder according to claim 1, characterized in that the front wall of the piston (3) has an obtuse c 8 (21) in the   the top of which opens the compensation hole (18).   8 master cylinder according to claim 1, characterized in that a sealing member (17) is housed in the front surface that the valve body (14) has opposite the compensation hole (18), this body d sealing having an outer diameter greater than the diameter of the compensating hole (18) and terminating in outcrop   of the front surface of the valve body (14).   Tandem master cylinder comprising, for the master cylinder piston, a captive return spring arranged between the piston and an intermediate piston according to claim 1, characterized in that the return spring (9) is prestressed more strongly than a return spring (9) for the intermediate piston (4), the latter return spring being arranged between the intermediate piston (4) and the bottom (2 a) of the cylinder, and the excess of prestressing of the first spring of reminder compared to the second corresponding to the force required for the   displacement of the intermediate piston (4).   My utre-cylinder according to claim 9, characterized in that the means (10, 11) for holding each captive return spring are fixed by their end remote from the valve body (14)   respectively at the bottom (2 a) of the cylinder and the intermediate piston (4).   Master cylinder according to claim 1, characterized in that the valve body (14) is provided with a plateau surface (14b) which, in the closed position, is sealingly applied against   the primary seal (6) of the master cylinder piston (3).   Master cylinder according to Claim 1, in tandem execution, characterized in that the valve body (14) of the piston (3) has a plateau surface (14b) which, in the closed position, is applied with sealing against the primary seal (6) of the piston (3), in that there is provided a valve opening spring (24) acting between the piston (3) and its valve body (14). ) and that the intermediate piston (4) has a thin central hole of   compensation (18) in front of which is the valve body (14).