FR2774344A1 - Pneumatic servomotor for vehicle braking assistance - Google Patents

Abstract

The servomotor comprises a rigid casing (3), formed by front (3a) and rear (3b) half shells, with a movable partition (4) delimiting front (5a) and rear (5b) chambers. It has a pneumatic piston (6) and a three way control valve (61), carried by the piston, selectively connecting the rear chamber to first (D) or second (A) pressure sources. The partition is able to be moved from a neutral position in which the rear chamber has a minimum volume to an activating position in which the rear chamber has a maximum volume.

Description

SERVOMOTOR WITH REDUCED VOLUME REAR CHAMBER
The present invention relates to a pneumatic brake booster for a motor vehicle, comprising. a front shell and a rear shell cooperating to define a rigid envelope, the rear shell having a cylindrical chimney; a movable partition sealingly delimiting a front chamber and a rear chamber inside the envelope, the front chamber being permanently connected to a first pressure source delivering a first pressure; a spring housed in the front chamber for urging the movable partition in a first axial direction oriented from the front chamber towards the rear chamber and placing the movable partition in a rest position; a pneumatic piston secured to the movable partition and mounted for sliding sliding in the chimney; and a three-way valve carried by the pneumatic piston and adapted to selectively connect the rear chamber to the first pressure source or to a second pressure source delivering a second pressure greater than the first, for moving the movable partition, according to a second reverse axial direction from the first axial direction, up to a maximum actuation position.

Devices of this type are well known in the prior art, as shown for example by US Patent 4,784,046.

Reducing the response time of braking devices is a constant concern in the automotive industry, and many effective solutions have already been envisaged for this purpose.

Although the invention also aims to propose a solution to this problem, its specificity is to propose a solution which can be used both alone and in combination with already known solutions, and the effects of which can thus be combined with the effects of solutions with which it is possibly associated.

To this end, the actuator of the invention is essentially characterized in that the rear chamber has, respectively, the rest position and, for the position of maximum actuation of the movable partition, of the first and second respective volumes, the first of which is at most equal to a tenth of the second.

Other characteristics and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limiting, with reference to the appended drawing, the sole figure of which is a sectional view of a compliant booster. to the invention.

The invention relates generally to a braking assistance device for a motor vehicle, essentially consisting of a pneumatic booster 1 actuating a master cylinder 2.

The booster comprises in a known manner a rigid casing 3, generally consisting exclusively of a front shell 3a and a rear shell 3b crimped one on the other along their periphery 3c.

The rear shell 3b has a cylindrical chimney 31, which is open to the atmosphere
AT.

Inside the envelope 3, a movable partition 4 sealingly defines at least one front chamber 5a and a rear chamber fb.

The movable partition 4 is integral with a pneumatic piston 6, which is mounted with sliding sliding in the chimney 31, and which closes it with respect to the atmosphere A.

A spring 7, housed in the front chamber 5a, biases the movable partition 4 in an axial direction Y-, the movable partition 4 thus adopting, in the absence of actuation of the booster, a rest position, which is that shown in solid lines in the figure.

A three-way valve 61, carried by the pneumatic piston 6, makes it possible to selectively connect the rear chamber 5b to the atmosphere A, or to a source of vacuum D to which the front chamber 5a is permanently connected.

The actuation of the servomotor is obtained by the application, on a control tiger 8, of a force oriented in the axial direction Y +, opposite to the axial direction Y-.

Under these conditions, the valve 61 connects the rear chamber 5b to the atmosphere A, and the movable partition 4, urged along the axial direction Y +, adopts a position, the most advanced of which is the maximum actuation position, partially shown in dotted lines. on the face.

As the front chambers 5a and rear 5b have volumes which are both complementary and variable, and as the rear chamber Sb fills up when the actuator is actuated, the chamber 5b has a minimum volume for the rest position of the movable partition 4, and a minimum volume for the maximum actuation position of this movable partition 4.

According to the invention, the minimum volume of the rear chamber Sb is at most equal to one tenth of the maximum volume of this same chamber 5b.

Thanks to this one characteristic. for example obtained by giving the movable partition a profile very close to that of: rear hood 3b, the rear chamber can be filled much more quickly than in the case of known servomotors, for which the ratio of the minimum volume of the rear chamber the maximum volume of this chamber is substantially greater, of the order of twice what is recommended by the present invention.

Claims (1)

 Claim Pneumatic brake booster for a motor vehicle, comprising: a front shell (3a) and a rear shell (3b) cooperating to define a rigid casing (3), the rear shell having a cylindrical chimney (3 1); a movable partition (4) sealingly delimiting a front chamber (5a) and a rear chamber (5b) inside the enclosure (3), the front chamber being permanently connected to a first pressure source (D ) delivering a first press; a spring (7) housed in the front chamber to urge the movable partition in a first axial direction (Y-) oriented from the front chamber towards the rear chamber and place the movable partition in a rest position, a pneumatic piston (6) integral with the movable partition (4) and mounted for sliding sliding in the chimney (31); and a three-way valve (61) carried by the pneumatic piston (6) and adapted to selectively connect the rear chamber (5b) to the first pressure source (D) or to a second pressure source (A) delivering a second pressure greater than the first, to move the movable partition, in a second axial direction (Y +) opposite to the first axial direction (Y-), until in a maximum actuation position, characterized in that the rear chamber has, respectively for the rest position and for the maximum actuation position of the movable partition (4), the first and second respective volumes, the first of which is at most equal to one tenth of the second.