WO2003004332A1

WO2003004332A1 - Pneumatic brake booster for emergency braking and method for controlling braking force

Info

Publication number: WO2003004332A1
Application number: PCT/FR2002/002116
Authority: WO
Inventors: Pierre Lebret; Marc Rambert
Original assignee: Robert Bosch Gmbh
Priority date: 2001-06-21
Filing date: 2002-06-19
Publication date: 2003-01-16
Also published as: FR2826325B1; FR2826325A1

Abstract

The invention concerns a pneumatic brake booster controlled by a valve (9) actuated by a plunger (8) housed in a pneumatic piston (5), said piston (5) being itself designed to apply a booster force collected by a reaction disc (13). The inventive brake booster further comprises an auxiliary pressure member (14) selectively pressing on the disc (13) and driven or not by the plunger (8), depending on the intensity of the actuating force applied thereon. The resulting brake booster provides a variable gain depending on the intensity of the actuating force, its response being particularly adapted to emergency braking situations.

Description

The present invention relates, in general, to - braking techniques for motor vehicles, using a pneumatic booster.

More specifically, the invention relates, according to a first of its aspects, a pneumatic brake booster comprising: a _. rigid envelope; a movable partition sealingly delimiting a front chamber and a rear chamber inside the rigid envelope, the front chamber ^' being connected in operation to a first pressure source delivering a first pressure, and the rear chamber being selectively connected to the front chamber or subjected to a pressure controlled by • selective communication with a second pressure source delivering a second pressure greater than the first; a pneumatic piston moving with the movable partition; adopting a control rod in a relative position dependent piston at least one actuating force ^selectively applied to the subsequent control rod an axial actuating direction oriented towards the front chamber, and an antagonistic restoring force oriented in an axial return direction; a plunger housed in the piston and driven by the control rod; a valve three ^'pathways controlling the pressure in the rear chamber, said valve selectively connecting the rear chamber to the front chamber or to the second pressure source, depending on whether the control rod- adopts relative to the piston relative position rest under the effect of at least the restoring force, or a relative actuation position under the effect of the actuating force; a resiliently deformable reaction disc thickness, a rear face of receiving at least the operating force applied by one face ^'end of the plunger, and a selectively applied assist force by an end face of the piston moved by a force at least exerted by controlled pressure on the movable partition, and of which one front face transmits a braking force resulting ^"in particular from the forces applied to the rear face of the disc

Devices of this type are well known in the prior art, as illustrated by example by patent documents US-3,470,697, FR-2,532,084, and FR-2,658,466.

Recent research has shown that drivers faced with an emergency braking situation tend to statistically underestimate the risks actually incurred, and therefore apply only insufficient braking force ^' to avoid the accident. .

This ^has' led to the development of various solutions aimed at overcoming the possible faulty behavior of an inexperienced driver or entered panic in an emergency.

In this context, the object of the invention is to propose a ^' simple solution to the problem posed by the control of the braking force when the latter reaches values which indicate the need not simply to slow down the vehicle gradually, but to stop it as soon as possible.

To this end, . the booster of the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that it further comprises an auxiliary support member, one front face of which is disposed opposite the rear face of the reaction disc for selectively exerting a pressing force therein, reversible retaining means capable of maintaining the auxiliary support member in a fixed relative position relative to the plunger as long as the actuating force is at more equal to a first determined threshold, and to allow movement of the auxiliary support member with respect to the plunger when the actuating force exceeds the first threshold, elastic return means for replacing the member auxiliary support in its position relative fixed at least for the relative rest position of the control rod, and a stop integral with the piston and selectively driving the auxiliary support member in the actuating direction when the actuating force exceeds a second determined threshold, greater than the first threshold.

It is possible to provide that, in the fixed relative position of the auxiliary support member with respect to the plunger, the front faces of the plunger and of the auxiliary support member are substantially coplanar or, alternatively, that the face front of the auxiliary support member is offset from the front face of the plunger in the axial direction of actuation. The auxiliary support member is advantageously disposed between the plunger and the piston, and has for example an annular shape allowing it to be disposed all around the plunger.

The reversible retaining means may comprise a groove formed in the auxiliary support member or in the plunger, and a stopper respectively, linked to the plunger or the auxiliary support member and elastically urged in the groove for the relative position. fixed of the auxiliary support member. As a variant, the reversible retaining means may comprise a pre-stressed spring exerting a retaining force urging the auxiliary support member towards its fixed relative position relative to the plunger.

In this case, the return means include the prestressed spring or are formed by it, while the reversible retaining means may further comprise a ramp of determined slope, kinematically linking the auxiliary support member to the plunger, and linking the retaining force at the first threshold of the actuating force by a trigonometric relationship involving the slope of this ramp. According to a second of its aspects, the invention relates to a method of controlling a braking force exerted by means of a pneumatic brake booster, this method comprising at least the operations consisting at least in applying a force d increasing actuation on a fraction of a first section of a deformable and substantially incompressible reaction element, to apply an increasing assistance force on another fraction of the first section of the reaction element, and to collect the force of thrust on a second section of the reaction element, this method being characterized in that the actuating force is applied to first and second fractions of the first section during a first time interval, during which the force d 'assistance is applied to a third ^' fraction of the first section, in that the actuating force is applied to the first fraction only nt of the first section during a second time interval, after the first and during which the assistance force continues to be applied to the third fraction of the first section, and in that the actuating force continues to be applied to the first fraction of the first section only during a third time interval, after the second and during which the assistance force is applied to the second and third fractions of the first section.

Prior to the first time interval, the actuating force can be applied to only one of the first and second fractions of the first section, the assistance force then being applied to the third fraction of the first section. This process can be carried out using, as a reaction element, a flat disc with faces rear and front respectively constitute the first and second sections.

Other characteristics and advantages of the invention will emerge clearly from the description which is given below, for information and in no way limitative, with reference to the appended drawings, in which:

- Figure 1 is a sectional view of a booster according to a first embodiment of the invention; ^' - Figure 2 is a detailed sectional view of part of the booster illustrated in Figure 1;

- Figures 3 to 7 are diagrams of the part of the booster illustrated in Figure 2, observed at different stages of operation of this booster; - Figure 8 is a diagram in arbitrary units representing the evolution of the braking force relative to the actuating force for the booster illustrated in Figure 1; and Figure 9 is a detailed sectional view similar to Figure 2, showing part of a booster according to a second embodiment of the invention.

A pneumatic booster according to the invention comprises so ^'known per se, a front shell and the rear shell 1b which together form a rigid casing. 1.

A movable partition 2 separates tightly

1 inside this rigid envelope 1 and delimits there

. front chamber 3 and a rear chamber 4, the front chamber 3 being in operation subjected to a first pressure Pd, relatively low.

A pneumatic piston 5 moves with the movable partition 2 and has a hub 6 slidably mounted in an opening 19 of a chimney of the casing 1. The servomotor is controlled by a control rod 7 movable in the hub 6 between a position rest (Figures 1, 2, 3 and 9) and a position extreme actuation (Figure 7), the position of this rod in the hub depending in particular on both an actuating force F11 + which is applied to this rod, in an axial direction of actuation X +, by the pedal brake (not shown), a return force Fil- exerted in the reverse direction X- at least by a main return spring 71, and a reaction force in the same direction as the return force.

A plunger 8, driven by the control rod 7, is slidably mounted in a bore 61 of the hub 6 to control the state of a three-way valve 9.

• this valve ^"9 (Figure 2) is substantially ^'consisting of an outer _seat. Annular device 91 formed at the periphery of the hub 6, an internal movable annular seat 92, which is concentric ^at peripheral seat 91 and carried by the plunger 8, and a tubular shutter 93, which is itself concentric with both the plunger and the hub.

L | tubular obturator 93 has an annular front face for closing intended to cooperate, as a function of the position of the control rod 7, therefore of the plunger 8, either with the internal seat 92 or with the external seat 91.

When the booster is at rest, the shutter 93 is applied to the internal seat 92 and isolates the rear chamber 4 from a pressure source, generally constituted by the atmosphere, which delivers a pressure Pa higher than the pressure Pd to which the front chamber is subjected 3. On the other hand, when an actuating force F11 + substantially greater than the restoring force Fil- of the spring 71 is exerted on the rod 7, this actuating force F11 + causes a displacement of the plunger 8 in the actuating direction X +, so that the shutter 93 comes off from the internal seat 92 by applying to the external seat 91, the rear chamber 4 then being connected to the pressure Pa and subject to a controlled pressure between the pressure values Pd and Pa.

The admission of air into the rear chamber pushes the movable partition 2 in, the direction of actuation X + and generates an assistance force F12 + which is exerted on the front face 51 of the piston 5.

The actuating force F11 + and the assisting force F12 + are applied, jointly, via a reaction disc 13, to actuate the master cylinder 20 illustrated in FIG. 1.

The reaction disc 13, which is made of a deformable and substantially incompressible material, for example an elastomer, is housed in a rigid cup 11, and receives at least, on its rear face 132, the actuating force F11 + which transmits the front face 81 of the plunger 8 to it, and the assistance force F12 + exerted by the front face 51 of the pneumatic piston 5.

The result of the forces exerted on the rear face 132 of the reaction disc 13, and which ultimately constitutes the braking force F2 + (FIGS. 5 to 7), is transmitted to the primary hydraulic piston 200 of the master cylinder 20 via the front face 131 of this disc 13, of the cup 11, and of a thrust rod 10 which is integral with the cup 11. Insofar as, due to the incompressibility of the reaction disc 13, all the forces of compression applied to this disc are in competition with each other, the application of the actuating force F11 + encounters an opposing reaction force, which varies with the assistance force F12 +, and which allows the driver to dose the actuation force it applies.

The device of the invention allows to vary the .gain the booster, that is to say, ^'the ratio of the braking force F2 at + F11 + actuating force, depending on the intensity of the force actuation F11 +. To do this, the booster of the invention essentially comprises, in addition to the components already described, an auxiliary support member 14, reversible retaining members 15 to 17, and elastic return means such as 16 or 18.

The auxiliary support member ^'14 has an end face 141 disposed opposite the rear face 132 of the reaction disk 13, this auxiliary support member being linked to conditionally plunger 8 to exert on the disc 13 a force of variable support.

The reversible retaining members 15 to 17, which will be detailed later, have the function of defining the conditions under which the auxiliary support member is linked to the plunger 8. More precisely, these reversible retaining members maintain the auxiliary support member 14 in a fixed relative position relative to the plunger 8 as long as the actuating force F11 + is less than or equal to a first determined threshold L1, and allow movement of the auxiliary support member 14 by relative to the plunger 8 when the actuating force F11 + exceeds this first threshold L1.

The means of. elastic return have the function of replacing the auxiliary support member 14 in its fixed relative position at least when the control rod 7 returns to its rest position relative to the piston 5.

This booster also includes a stop 62, which is integral with the piston 5, and which drives the member. auxiliary support 14 in the actuating direction X + when the actuating force F11 + exceeds a second determined threshold L2, greater than the first threshold L1.

When the auxiliary support member 14 is in its fixed relative position relative to the plunger 8, the respective front faces 81 and 141 of the plunger 8 and of the auxiliary support member 14 may be substantially coplanar, as shown by example Figure 2. However, it is also possible, as a variant, to provide that the front face 141 of the auxiliary support member 14 is then offset with respect to the front face 81 of the plunger 8 ^' in the axial direction of actuation X +, as shown in Figure 9.

The auxiliary support member 14 for example takes the form of an annular sleeve, disposed around the plunger 8, and therefore interposed between this plunger 8 and the piston 5.

In the embodiment of FIG. 2, the reversible retaining means 15 comprise a groove 150, for example made in the auxiliary support member 14, balls such as 151, which are engaged in an internal groove 143 of the organ auxiliary support 14, and an elastic ring .fendue 152. the internal groove 143 take ^'the form of a split torus, nearly half a torus.

When the auxiliary support member 14 is in its fixed relative position relative to the piston 5, as illustrated in FIG. 2, the split ring 152, for example made of spring steel, resiliently biases the balls 151 in the groove 150, these balls thus fulfilling a stopper function.

. Furthermore, a return spring 18 is interposed between the rear part of the plunger 8 and the auxiliary support member 14 to replace the latter in the fixed relative position illustrated in FIG. 2 when the control rod 7 returns to its position. rest.

In the embodiment of FIG. 9, the reversible retaining means essentially comprise a prestressed spring 16, and a mechanical system 17 making it possible to reduce to a component of the actuating force F11 + the force exerted between the plunger and the auxiliary support member 14 and which tends to move the auxiliary support member 14 from its fixed relative position.

The prestressed spring 16, which has the function of exerting a retaining force urging the member auxiliary support 14 towards its fixed relative position relative to the plunger 8, is in this case a prestressed spring in torsion between a fixed point 142 of the auxiliary support member 14 and a washer 171 disposed between the plunger 8 and the auxiliary support member 14.

The washer is rotatably mounted around the plunger 8 by means of rolling balls 21 interposed between the washer 171 and a stop 83 of the plunger 8, this stop also serving to block the movement of the member 14 in the actuating direction X + beyond its fixed position.

The washer 171 carries several lugs such as 172, engaged in identical respective helical ramps 170 having the same angle slope Alpha relative to the actuation direction X +.

Preferably, the plunger 8 and the auxiliary member 14 are made integral with one another in rotation by means of complementary reliefs 89 and 149, indented one inside the other.

When the actuating force and the reaction force tend to move the auxiliary support member 14 from its fixed position relative to the plunger 8, the stop 83 presses on the rolling balls 21, which in turn press on the washer 171, which can only move relative to the member 14 by following the ramp 170 and by increasing the torsional stress of the spring 16.

Under these conditions, the auxiliary support member 14 can leave its fixed position only when the ratio of the actuating force F11 + to the preload of the spring 16 reaches the value of the tangent of the angle Alpha, this trigonometric relationship making it possible to obtain a relatively high threshold L1 for releasing the support member 14 relative to the plunger 8 despite the use of a spring 16 of relatively modest stiffness. The operation of the booster of the invention is illustrated in FIGS. 3 to 8 with reference to the embodiment illustrated in FIG. 2.

At rest, the respective front faces 81 and 141 of the plunger 8 and the auxiliary member 14 are spaced from the rear face 132 of the disc 13 (FIG. 3).

The application of an actuating force F11 + initially causes (FIG. 4) the simultaneous displacement of the plunger 8 and the auxiliary member 14 without any other consequence than the compression of the return spring 71.

Like this . spring 71 is prestressed, such displacement is only possible when the actuating force F11 + exceeds (FIG. 8) a minimum value L00 which is not zero. As soon as the actuating force F11 + reaches a value L0 of start of assistance (FIG. 8), the valve 9 opens (FIG. 5) and the pressure in the rear chamber 4 increases, which produces a displacement of the partition. mobile 2 in the direction of actuation X +. The front face 51 of the piston 5 then presses on the disc 13, which deforms, and the rear face 132 of which comes into contact with the front faces' 81 and 141 of the plunger 8 and of the auxiliary member 14.

Under these conditions, the respective end faces of the plunger 81 ^'8, 141 of the auxiliary member 14 and 51 of the piston 5 are appui- through their respective surfaces SI, S2, and S3 on the rear face 132 of the disc 13.

As moreover the plunger 8 and the auxiliary member 14 are integral with one another, and as the disc 13 is incompressible, the gain of the booster, immediately beyond the value L0 of .the actuating force (Figure 8), is equal to (S1 + S2 + -S3) / (S1 + S2). ^' As soon as the actuating force F11 + exceeds a first threshold L1 (Figures 6 and 8), the retaining force exerted by the balls 151 on the rear edge of the groove 150 is overcome by the actuating force F11 +, so that the auxiliary member 14 becomes detached from the plunger 8 and no longer exerts any significant pressure on the disc 13. If the reaction disc 13 is then always subjected to the input force exerted on the surface SI and with the assistance force exerted on the surface S3, on the other hand it must fill the volume suddenly left free by the auxiliary support member 14 and limited by the stop 62.

As a result, to the reaction disk 13, a similar transition ^'to that of a jump, in which the gain, then not only dependent on the surfaces SI, S2 and S3, but also the stiffness of the rubber which is consisting disc ^'13, continues to rise as shown in Figure 8.

When the actuating force F11 + reaches a second threshold L2 (Figures 7 and 8), the stop 62 of the piston 5 joins the auxiliary member 14 and applies it to the disc 13, this member 14 then moving integrally with the piston 5 and participating in the application on disk 13 of the assistance force.

Under these conditions (Figure 8), the gain of the servomotor increases again by taking a new value equal to (S1 + S2 + S3) / (SI).

When the pressure in the rear chamber 4 reaches the value Pa, which occurs for a value L3 of the actuating force F11 +, the subsequent increase in the braking force F2 + follows the increase in the actuating force, the actuator then being in saturation mode.

When the actuating force F11 + decreases, the valve 9 closes, the rear chamber 4 empties through the front chamber 3, and the braking force evolves to a zero value following, in known manner, the upper curve from the diagram in Figure 8 such that Ca and Cb, or Ca and Cb ', the spring 18 replacing the auxiliary member in the position illustrated in FIG. 2.

Claims

1. Pneumatic brake booster comprising: a rigid casing (1); a movable partition

(2) sealingly delimiting a front chamber (3) and a rear chamber (4) inside the rigid envelope (1), the front chamber (3) being connected in operation to a first pressure source delivering a first press (Pd), and the rear chamber ^' (4) being selectively connected to the front chamber

(3) or subjected to a pressure controlled by selective communication ^• with a second pressure source delivering a second pressure (Pa) greater than the first (Pd); a pneumatic piston (5) moving with the movable partition (2); a control rod (7) adopting in the piston (5) a relative position depending at least on an actuating force (F11 +) selectively applied to the control rod (7) in an axial actuation direction (X +) oriented towards the front chamber (3), and with an opposing restoring force (F11-) oriented in an axial return direction (X-); a plunger (8) housed in the piston (5) and driven by the control rod (7); a - - three-way valve (9) controlling the pressure in the rear chamber (4), this valve (9) selectively connecting the rear chamber (4) to the front chamber (3), or to the second pressure source (Pa), depending on whether the control rod (7) assumes with respect to the piston (5) relative rest position under the effect of at least the return force ^(Fll-j, or a relative position actuation under the effect of the actuating force (F11 +); a reaction disc (13) elastically deformable in thickness, one rear face (132) of which receives at least the actuating force (F11 +) applied by a front face ( 81) of the plunger (8), and an assistance force (F12 +) selectively applied by a front face (51) of the piston (5) moved by at least one force exerted by controlled pressure on the movable partition

(2), and a front face (131) of which transmits a braking force (F2 +) resulting in particular from the forces applied to the rear face (132) of the disc (13), characterized in

5 which further comprises an auxiliary support member

(14) of which a front face (141) is disposed opposite the rear face (132) of the reaction disc (13) in order to selectively exert a pressing force thereon, reversible retaining means (15 to 17) proper to maintain the organ

1 _. 0 auxiliary support (14) in a fixed relative position relative to the plunger (8) as long as the actuating force (F11 +) is at most equal to a first determined threshold (L1), and to allow movement of the auxiliary support member (14) relative to the plunger

15 (8) when the actuating force (F11 +) exceeds the first threshold (L1) ^" , elastic return means (16, 18) for replacing the auxiliary support member (14) in its relative fixed position at less for the relative rest position of the control rod (7), and a 0 stop (62) integral with the piston (5) and selectively driving the auxiliary support member (14) in the actuating direction (X + ) when the actuating force (F11 +) exceeds a determined second threshold (L2), greater than the first threshold (L1).

2. Booster according to 'claim 1, characterized in that, in the fixed relative position of the auxiliary support member (14) relative to. plunger (8), the front faces (81, 141) of the plunger (8) and of the auxiliary support member (14) are substantially 0 coplanar.

3. ^• Booster according to claim 1, characterized in that, in the fixed relative position of the auxiliary support member (14) relative to the plunger (8), the front face (141) of the member 5 auxiliary support (14) is offset from the front face (81) of the plunger (8) in the axial direction of actuation (X +).

4. Booster according to any one of the preceding claims, characterized in that the auxiliary support member (14) has an annular shape, and in that it is arranged around the plunger (8).

5. Booster according to any one of the preceding claims, characterized in that the auxiliary support member (14) is disposed between the plunger (8) and the piston (5).

6. Booster according to any one of the preceding claims, characterized in that the reversible retaining means (15 to 17) comprise at least one groove (150) formed in the auxiliary support member ( _. 14) or in the plunger (8), and at least one retainer (151) respectively linked to the plunger (8) or to the auxiliary support member (14) and elastically urged in the groove (150) for the fixed relative position of the auxiliary support member (14).

7. Booster according to any one of claims 1 to 5, characterized in that the reversible retaining means (15 to 17) comprise a prestressed spring (16) exerting a retaining force urging the auxiliary support member (14 ) .to its fixed relative position relative to the plunger (8).

8. Booster according to claim 7, characterized in that the reversible retaining means

(15 to 17) comprise a ramp (170) of determined slope (Alpha}, kinematically linking the auxiliary support member (14) to the plunger (8), and linking the retaining force to the first threshold (Ll) of the actuation force by a trigonometric relationship involving the slope (Alpha) of this ramp.

9. Method for controlling a braking force (F2 +) exerted by means of a pneumatic brake booster, this method comprising at least the operations consisting in at least applying an increasing actuation force (F11 +) on a fraction (IF) of a ^'first section (132) of a reaction member (13) deformable and substantially incompressible, applying an increasing assistance force (F12 +) on another fraction (S3) of the first section (132) of the reaction element (13), and collecting the braking force (F2 +) on a second section (131) of the reaction element (13), characterized in that the actuating force (F11 +) is applied to first and second fractions (SI, S2) of the first section ( 132) during a first time interval, during which the assistance force (F12 +) is applied to a third fraction (S3) of the first section (132), in that the actuation force (F11 +) is applied to the first fraction (SI) only of the first section (132) during a second time interval, subsequent to the first and during which the assistance force (F12 +) continues to be applied to the third fraction. (S3) of the first section (132), and in that the actuating force (F11 +) continues to be applied to the first fraction (SI) of the first section (132) only during a third, later time interval in the second and during which the assistance force (F12 +) is applied to the second and third fractions (SI, S2) of the first section (132).

10. Method according to claim 9, characterized in that. that the actuating force is applied to only one of the first and second fractions (S1, S2) of the first section (132) prior to the first time interval, the assistance force (F12 +) then being applied to the third fraction (S3) of the first section (132).

11. Method according to claim 9 or 10, characterized in that the reaction element (13) is a flat disc, of which rear and front faces (132, 131) respectively constitute the first and second sections (132, 131) .