Pneumatic servo with symmetric casing

Details Pneumatic servo with symmetric casing Pneumatic servo with symmetric casing

1995-03-01

1999-11-02

Denion, Thomas E.

Motors: expansible chamber type

Working member position feedback to motive fluid control

Follower type

921691, 913692, F15B 910

Patent

active

059749440

DESCRIPTION:

BRIEF SUMMARY
The subject of the present invention is a pneumatic servo, of the type of those which are used to provide assistance with braking of motor vehicles.


BACKGROUND OF THE INVENTION

Such servos conventionally include a casing including a cylinder and a cover having an axis of symmetry, the inside of the casing being divided in leaktight fashion by a movable wall structure into a front chamber permanently connected to a source of partial vacuum, and a rear chamber connected selectively to the front chamber or to a source of pressure by a three-way valve located in a rear tubular part of the movable wall structure sliding in a leaktight fashion in the cover and actuated by a control rod.
Very many documents relate to this type of pneumatic servo. In all these known embodiments, the casing of the servo is typically formed of a front half-shell, also termed cylinder, and of a rear half-shell, also termed cover, the cylinder and cover being secured to one another by crimping, trapping between them an outer peripheral bead of the unrolling diaphragm providing sealing between the front and rear chambers.
The cover is conventionally intended to be fixed to the bulkhead of the vehicle, on the engine compartment side, and includes an axial cylindrical extension, also termed shaft, pointing toward the rear and penetrating into the passenger compartment of the vehicle. This shaft receives, with leaktight sliding, the rear tubular part of the movable wall structure containing the three-way valve.
The cylinder for its part includes a plane face around the axis of symmetry of the servo, which face is intended to receive a fastening flange of a master cylinder, actuated by a pushrod secured to the movable wall structure of the servo, when the latter is actuated.
It follows that the cylinder and the cover, together constituting the casing of the servo, form two different components. This implies that the time of design, manufacture, storage and management costs are multiplied by two. In particular, the cover including the shaft described above constitutes a component which is quite tricky and expensive to manufacture owing to its complex shape, rejects on the production or assembly line not being negligible.


SUMMARY OF THE INVENTION

The object of the present invention is therefore to solve this problem by proposing a servo for which the costs of manufacturing the casing are reduced to a large extent.
To this end, the invention proposes a servo of the type recalled hereinabove, in which the cylinder and the cover of the servo are made of two identical half-shells.


DETAILED DESCRIPTION OF THE INVENTION

Other objects, characteristics and advantages of the present invention will emerge clearly from the description which will follow of an embodiment given by way of non-limiting example, with reference to the appended drawings in which:
FIG. 1 represents a side view in transverse section of a pneumatic servo for assisting with braking produced according to the present invention;
FIGS. 2 and 3 represent perspective views of the half-shells forming the casing of the servo of FIG. 1;
FIG. 4 represents a half side view of the servo of FIG. 1;
FIG. 5 represents an enlarged partial view of a longitudinal section of the servo along the line V--V of FIG. 4;
FIG. 6 represents a sectional view of a variant of the non-return valve equipping the servo of FIG. 1, and
FIG. 7 represents a view similar to that of FIG. 5 of an embodiment variant of the half-shells forming the casing of the servo.
FIG. 1 represents, in section, a pneumatic servo for assisting with braking, designed to be placed in the usual way between the brake pedal of a vehicle and the master cylinder controlling the braking circuit of this vehicle. By convention, that part of the servo which points toward the master cylinder is termed the "front", and that part of the servo which points toward the brake pedal is termed the "rear". In FIG. 1, the front is thus to the left and the rear to the right.
The servo represented comprises an outer casing 10 in the form of a shell,

REFERENCES:
patent: 4256016 (1981-03-01), Thomas
patent: 4604944 (1986-08-01), Tsubouchi

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