FR2765171A1 - Power assisted braking system master cylinder with hydraulic reaction, used for vehicles - Google Patents

Abstract

The master cylinder consists of a housing with a main bore containing a piston (12) with a secondary bore and a reaction piston (3) with one end (31) receiving an actuating force and the other sliding in the secondary bore to form a reaction chamber (4) in communication with the servomotor's working chamber. The servomotor has a first shut-off seat (41) formed on a front face of the reaction piston's second end (32), a second shut-off seat (42) on the first end (7a) of a support (7) located in the reaction chamber at a distance from the first seat at least equal to the minimal stroke amplitude, and a spring (51) which maintains the spacing between the two seats.

Description

HYDRAULIC REACTION MASTER CYLINDER

DYNAMICALLY CANCELABLE

  The present invention relates to a hydraulic reaction master cylinder for a pneumatic brake booster, comprising: a body pierced with a main bore; a cylindrical main piston, pierced with a secondary bore, and one end of which is external to the body and is capable of receiving an assistance force oriented in a first direction, this main piston being mounted in leaktight sliding in the main bore to delimit therein a working chamber subjected in operation to hydraulic pressure; and a reaction piston, a first end of which is external to the body and is capable of receiving an actuating force oriented in the first direction, and a second end of which is mounted to slide in the secondary bore to delimit a reaction chamber which communicates with the working chamber, the reaction piston being able to move, relative to the main piston, over a stroke of minimum amplitude not zero

  for a gradient of the actuating force greater than a determined threshold.

  A master cylinder of this type is for example described in patent FR-2,724,354.

  Devices of this type have been developed very recently for their ability to overcome

  dynamic faults in pneumatic brake booster motors.

  It is known in fact that pneumatic brake booster motors, which are used to provide a braking assistance force in addition to the actuating force exerted by the driver on the brake pedal and in theory proportional to this last, present the defect of being able to develop this assistance force only after a certain delay compared

to the actuating force.

  As the assistance force results from a difference between the pneumatic pressures prevailing respectively in a front chamber of the booster, connected to a source of vacuum, and in a rear chamber, connected to the atmosphere during braking, and as the delay of the assistance force on the actuation force is due to a limitation of the flow of atmospheric air admitted into the rear chamber through the inlet valve of the actuator at the time of

  braking, this delay is all the more important as the braking is abrupt.

  However, situations in which braking is rapid are generally emergency situations, in which the driver on the contrary would need precisely, as soon as possible, the

  greatest assistance force possible.

  These considerations have led, quite recently, to the development of master cylinders with hydraulic reaction allowing on the one hand a greater amplitude of opening of the inlet valve of the booster, therefore an increased air flow, and on the other hand a dynamic modulation of the reaction force, that is to say a modulation, as a function of the braking speed, of the fraction of the assistance force that the reaction master cylinder opposes to the force

  actuation to adjust the assistance force as a function of this actuation force.

  Thanks to devices described in unpublished documents, it is thus possible to considerably reduce the reaction force in the event of emergency braking compared to the value which it presents in the case of normal braking, which allows correlatively to increase the

  braking force available in emergency braking situations.

  However, a problem still encountered in the development of these devices is the

  difficulty canceling the reaction force in the event of severe braking.

  The purpose of the pn -sente invention is to propose a solution to this problem. , ..

  To this end, the master cylinder of the invention, furthermore in accordance with the preamble above, is essentially characterized in that it further comprises: a first obturation seat formed on a front face of the second end of the reaction piston; a second closure seat carried by the main piston and disposed in the reaction chamber, at a distance from the first closure seat at most equal to the stroke of minimum amplitude; and at least one first spring urging the reaction piston in a direction suitable for spreading the first seat

  the second shutter seat.

  In a very elaborate embodiment of the invention, the secondary bore is stepped, and the reaction piston comprises a pusher element, an annular element surrounding the pusher element, and a tubular element following the following pusher element the first direction,

  the first obturation seat then being formed on the tubular element.

  It is also possible to ensure that the response curve of the servomotor equipped with the master cylinder of the invention has, as is conventionally the case, an initial jump, by providing that this master cylinder with hydraulic reaction includes a second spring urging a movable ring in the first direction against an internal support of the secondary bore, and that the reaction piston has means for driving the movable ring when it is moved, from a rest position, according to a reverse direction of the

first direction.

  Other characteristics and advantages of the invention will emerge clearly from the description

  which is made of it below, by way of indication and in no way limitative, with reference to the appended drawings, in which: - Figure 1 is an overall sectional view of a booster incorporating the master cylinder of the invention; - Figure 2 is an enlarged sectional view of the part of the master cylinder in which the advantageous features of the invention are concentrated, for a first embodiment of the latter; and - Figure 3 is an enlarged sectional view of the part of the master cylinder in which the advantageous characteristics of the invention are concentrated, for a second mode of

realization of the latter.

  As indicated above, the invention relates to a master cylinder with hydraulic reaction

  I intended to equip a pneumatic brake booster 2.

  In a manner known per se, the pneumatic assistance booster comprises (FIG. 1) a rigid casing 21, a movable partition 22 comprising a rigid skirt 23, a pneumatic piston 24, a three-way valve 25, and a control rod 26 operated by a

  brake pedal (not shown).

  -2- D The mobile partition 22 sealingly separates the interior volume of the rigid envelope 21 in

  two pneumatic chambers C1 and C2, of complementary and variable volume.

  The first chamber, or front chamber C1 is connected to a low pressure source D via a non-return valve 28, and the second chamber, or rear chamber C2 is capable of being selectively connected, to the by means of the three-way valve 25, either at the low pressure source D or at a relatively high pressure source A, for example the atmosphere. Thanks to this arrangement known per se, the actuation of the three-way valve 25, which makes it possible to connect the rear chamber C2 to the second source A, causes a pressure difference between the front and rear chambers Cl and C2, the movable partition 22 thus being solicited by a force which represents the assistance force of the servomotor, and moving inside

envelope 21.

  In practice, the three-way valve 25 is carried by the piston 24 and its opening on the rear chamber is controlled by the application of an actuating force in the axial direction X + on the control rod 26, this rod being itself carried by the piston 24 and is

ending with a probe 29.

  The master cylinder 1 is arranged in the extension of the control rod 26 and essentially comprises a body 11 from which protrude a main piston 12 and a reaction piston 3, this reaction piston being part of hydraulic reaction means which will be detailed.

  which are more specifically the subject of the invention.

  The body 11 is pierced with a main bore 110, in which the main piston 12, of cylindrical shape and pierced with a secondary bore 120 possibly stepped, is slidably mounted in leaktight manner to delimit therein a working chamber 13 subjected to operation to one

hydraulic pressure.

  The end 121 of the main piston 12, which is outside the body 11, provides support for the pneumatic piston 24, so as to receive the assistance force transmitted to this pneumatic piston 24 by the movable partition 22 in its together, and oriented in the direction

axial X +.

  Similarly, a first end 31 of the reaction piston 3, which is located outside the body 11, provides support for the probe 29 to receive the actuating force exerted by the conductor in the axial direction X + and transmitted by the control rod 26. The other end 32 of the reaction piston 3 is mounted to slide in the secondary bore 120 to delimit a reaction chamber 4 which communicates with the chamber

  13, for example through channels such as 124.

  Given the delay with which the assistance force develops relative to the actuating force in the event of sudden braking, the reaction piston 3 is liable to move, relative to the main piston 12, over a stroke of minimum amplitude K when the temporal variation of the actuating force exceeds a predetermined threshold, from which

  braking can be considered as emergency braking.

  -3 - The hydraulic reaction means which are more particularly the object of the invention (FIG. 2) essentially comprise, in addition to the reaction piston 3, a first obturation seat 41, a second obturation seat 42, and at least one first spring 51 The first obturation seat 41, which is formed on a front face 33 of the second end 32 of the reaction piston 3, is intended to come to cooperate with the second obturation seat 42, which is carried by the main piston 12 and which is disposed in the reaction chamber 4, this second seat being for example formed on an axial piece 7 screwed onto the

  second end 122 of the main piston 12 and carrying the channels 124.

  The maximum distance separating the first obturation seat 41 from the second obturation seat 42, that is to say in practice the distance which separates these two seats in the rest position of the master cylinder, as shown in FIG. Figure 2 is at most equal to the stroke K, so as to allow the first seat 41 to come to be applied to the second seat 42 in the event of emergency braking. The first spring 51, which has the function of urging the reaction piston 3 in a direction suitable for spreading the first obturation seat 41 from the second obturation seat 42, is for example a spring working in compression and installed between the part axial 7 and the piston of

reaction 3.

  It may also be advantageous, to reproduce the known feeling of a brake pedal, to provide a second spring 52 urging a movable ring 6 in the direction X + against an internal support 123 of the secondary bore, the reaction piston 3 comprising means, such as a shoulder 34, for driving the movable ring 6 when it is moved, from its rest position shown in FIG. 2, in a direction X- opposite to the direction

of actuation X +.

  The operation of the master cylinder of the invention is as follows.

  When a relatively slowly varying actuating force is applied to the control rod 26, the depression of the probe 29 causes the valve 25 to open, thus admitting atmospheric air into the rear chamber C2, before the reaction piston 3

  could have applied the shutter seat 41 to the second seat 42.

  Under these conditions, the movable partition 22 exerts on the end 121 of the main piston 12 an assistance force which moves the main piston in the direction X + and which opposes any relative movement of the reaction piston 3 relative to the piston main 12 following the

  direction X +, therefore prohibits contact between seats 41 and 42.

  In this operating mode, the hydraulic pressure, which prevails in the working chamber 13 and in the reaction chamber 4, and which therefore acts on the entire section SI of the end 32 of the reaction piston 3, ends up by push back the reaction piston 3 and the ring 6 by compressing the spring 52, and thus shows on the probe 29 a reaction force whose intensity is that of the reaction forces conventionally used in known servomotors. When a relatively rapidly varying actuating force is applied to the control rod 26, the reaction piston 3 on the other hand allows the first obturation seat -4- 41 to come to bear on the second seat 42 before atmospheric air can be admitted into the rear chamber C2 in sufficient quantity for the movable partition 22 to exert on the end 121 of the main piston 12 an assistance force capable of moving the main piston in the direction X + and to make up for the movement of the reaction piston 3 ...., However, as the first seat 41 is then applied to the second seat 42, and since the mutual overlap section of these two seats is by definition equal to the section S1 of the end 32 of the reaction piston 3, the hydraulic pressure prevailing in the working chamber 13 and in the reaction chamber 4 ceases, in this operating mode, to be able

  exert any reaction force on the reaction piston 3.

  It is therefore thus possible, thanks to the invention, to cancel or practically cancel the reaction force which opposes the actuating force exerted on the reaction piston 3 in the event of rapid application of this force. actuation, therefore increasing the actuation force

  available in emergency braking situations.

  FIG. 3 illustrates the inventive concept in the case of the use of a more complex reaction piston, already allowing, in itself, two different modes of hydraulic reaction, these

  two modes nevertheless being external to the specific object of the present invention.

  In this case, the secondary bore 120 of the main piston 12 is stepped and the reaction piston 3 comprises in particular a pusher element 3a, an annular element 3b surrounding the pusher element, and a stepped tubular element 3c disposed beyond the push element 3a with respect to

to the first direction X +.

  Such a reaction piston can, by construction, allow either the appearance of a reaction force applying to the cumulative section S2 of the pusher element 3a and of the annular element 3b, in which the ring 6 can be integrated , or, by closing a hydraulic valve arranged between the pusher element 3a and the tubular element 3c, the appearance of a force of

  reaction applying only on section S 1 of the end 32 of the reaction piston 3.

  The application of the inventive concept to this arrangement, thus leading to providing the first obturation seat 41 on the tubular element 3c and a second seat 42 similar to that of the first embodiment illustrated in FIG. 2, thus makes it possible to cancel, in this second mode of

  realization also, the reaction force in case of emergency braking.

-5-

Claims (3)

  1. Hydraulic reaction master cylinder for servomotor. brake assist tire, comprising: a body (11) pierced with a main bore (110); a cylindrical main piston (12), pierced with a secondary bore (120), and one end (121) of which is external to the body, is capable of receiving an assistance force oriented in a first direction (X +), this main piston being mounted slidingly sealed in the main bore to delimit therein a working chamber (13) subjected in operation to hydraulic pressure; and a reaction piston (3) of which a first end (31) external to the body is capable of receiving an actuating force oriented in the first direction (X +), and of which a second end (32) is mounted for sliding sliding in the secondary bore (120) to delimit therein a reaction chamber (4) which communicates with the working chamber (13), the reaction piston (3) being able to move, relative to the main piston (12), on a stroke (K) of non-zero minimum amplitude for a gradient of the actuation force greater than a determined threshold; characterized in that it further comprises: a first closure seat (41) formed on a front face (33) of the second end (32) of the reaction piston (3); a second closure seat (42) carried by the main piston (12) and disposed in the reaction chamber (4), at a distance from the first closure seat (41) at most equal to said stroke of minimum amplitude ; and at least one first spring (51) biasing the reaction piston (3) in one direction   able to separate the first shutter seat (41) from the second shutter seat (42).   2. Master cylinder with hydraulic reaction according to claim 1, characterized in that the secondary bore (120) is stepped and in that the reaction piston (3) comprises a pusher element (3a), an annular element (3b ) surrounding the pusher element, and a tubular element (3c) following the pusher element in the first direction (X +), the first seat   shutter (41) then being formed on the tubular element.   3. Hydraulic reaction master cylinder according to any one of claims   above, characterized in that it comprises a second spring (52) urging a movable ring (6) in the first direction (X +) against an internal support (123) of the secondary bore, and in that the piston reaction (3, 3b) comprises means (34) for driving the movable ring (6) when it is moved, from a rest position, according to a second   direction (X-) opposite of the first direction (X +). -6-