GB2064651A

GB2064651A - An Inside Vent Device for Pneumomechanical Braking Cylinders in Vehicle Braking Systems

Info

Publication number: GB2064651A
Application number: GB8035613A
Authority: GB
Original assignee: Fabbrica Italiana Magneti Marelli SpA; Magneti Marelli SpA
Current assignee: Industrie Magneti Marelli SRL; Marelli Europe SpA
Priority date: 1979-11-28
Filing date: 1980-11-05
Publication date: 1981-06-17
Also published as: IT1127628B; FR2471306A1; DE3040691A1; IT7927628A0; FR2471306B1; GB2064651B

Abstract

A vent or bleeding device is provided in a braking cylinder having a spring (8) operated mechanical actuator (B) for parking braking and a pneumatic actuator (A) for duty braking. The vent to atmosphere of the housing chamber (12) for the spring (8) is effected through the interior (14) of the hollow stem (9) of the pneumatic actuator (A) and connection A1. A lip seal or gasket (15-15a) is mounted on a closure plug (17) of the end portion (9a) of said hollow stem (9), which allows the passage of vent air from said housing chamber for the spring, while precluding the passage in the opposite direction during duty braking. <IMAGE>

Description

SPECIFICATION An Inside Vent Device for Pneumomechanical Braking Cylinders in Vehicle Braking Systems This invention relates to inside vent devices for pneumomechanical braking cylinders in vehicle braking systems, and more particularly to devices for venting to atmosphere the chamber housing the mechanical actuator spring through the interior of the hollow stem of said actuator and the supply chamber for the pneumatic actuator.

As well known, pneumomechanical braking cylinders comprise two coaxial actuators, of which one under pneumatic control for duty braking, and the other under mechanical control for vehicle aid or parking braking.

A pneumatic actuator comprises a membrane plunger or piston directly acting upon the operating members of the brakes, whereas a mechanical actuator comprises a plunger or piston which is normally subjected at one side to the pressure action, and at the other side to the action.of a compressed spring acting through its stem on said operating members of the brakes, not directly, but through the membrane of said pneumatic actuator.

During duty braking, air is fed into the supply chamber of the pneumatic actuator, which causes the displacement of the membrane plunger or piston, and accordingly the operation of the braking members.

On the other hand, to provide for aid or parking braking, the supply chamber of the mechanical actuator is vented or bleeded, so that by being stretched said compressed spring transmits the strain through the actuator stem to the membrane, and as a result to the brake operating members.

Known are inside vent devices of the above mentioned type, which allow an indirect communication between the chamber housing the mechanical actuator spring and atmosphere, thus protecting such a chamber from dust, water and atmospherical agents.

Such devices would normally comprise a check valve located on the end portion of the hollow stem, providing a passage between the spring chamber and the supply chamber of the pneumatic actuator.

The valve is held at passage open position by the membrane of the pneumatic actuator against the action of a preloaded spring.

Accordingly, its operation is not reliable because depending on the membrane thrust in one direction and spring stretching in the other direction. Additionally such a valve requires a very precise housing and accordingly costly accurate working or processing operations.

It is the object of the present invention to provide an inside vent device, the operation of which will not depend on the intervention of further members, and which is very simple, reliable and of low cost.

According to the invention, this is achieved by a venting device characterized by a undirectional or one-way valve inserted within the hollow stem of the mechanical actuator, this valve allowing the communication between the spring housing chamber of said mechanical actuator and the supply chamber of the pneumatic actuator as said spring is being compressed, while shutting off such a communication when the duty braking is being operated.

According to a preferred embodiment, such a undirectional or one-way valve comprises an annular lip seal or gasket, retained within a seat formed in a closure plug of the end portion of said hollow stem, the lip of which sealingly adheres to the inner surface of the stem, so as to preclude any air passage from the supply chamber of the pneumatic actuator to the spring housing chamber when the vehicle driver operates the pedal of the duty brake, while being separated therefrom, so as to allow said spring housing chamber to be vented into said supply chamber of the pneumatic actuator and therefrom to atmosphere, when said spring is compressed due to the displacement of the relative plunger or piston as it is brought back to unbraking position of the vehicle.

The further features and details of the invention will become more apparent frdm the following description with reference to the accompanying drawings, in which: Fig. 1 is an axial sectional view showing the pneumomechanical braking cylinder provided with a venting device according to the invention; and Fig. 2 is an enlarged view of the venting device shown in Fig. 1.

Referring to Fig. 1, reference letter A designates the pneumatic actuator for the braking cylinder and reference letter B designates the coaxial mechanical actuator.

Conventionally, this actuator A comprises a membrane plunger or piston 1 acting through a cap 2 on the stem 3 transmitting the braking force or strain to the brake operating members (not shown).

This actuator is normally operated during duty braking, as provided by supplying air into the supply chamber 4 through the connection Al on operation of the brake pedal.

The mechanical actuator B, separated by the above mentioned actuator A by means of wall 5, comprises a plunger or piston 6 which is normally subjected at one side to the pressure air in supply chamber 7, and at other side to the action of a compressed spring 8.

This plunger or piston 6 has a hollow stem 9 sealingly sliding within a collar 5a of wall 5 and by its free end 9a teminates in the above mentioned chamber 4. The other end 9b of the hollow stem is connected to said plunger or piston 6 by force or push fit in a collar 6a of the latter.

The mechanical actuator B is operated during vehicle aid or parking braking, which braking is provided by bleeding or venting said chamber 7 through a connection B1 on operation of a hand distributor or hand lever (not shown).

Through such a vent, said spring 8 is allowed to stretch out and hence to urge the assembly comprising said plunger or piston 6 and stem 9 which, therefore, will act upon membrane 1, causing the above mentioned parking braking.

In order to move said piston-stem assembly back to the vehicle unbraking position (such as that shown in the drawing), it is necessary either to deliver air into said chamber 7 through said connection B1, or to manually operate screw 10.

In this latter case, said stem 9 and plunger or piston 6 are moved back to the position shown in the drawing head 11, which is secured to the inner end of screw 10 and is upward drawn during the rotation of the latter.

At this stage, at which said spring 8 is compressed, air in chamber 12 is vented to atmosphere through the annular passage 13 between said screw 10 and collars 6a, 9b, the inside 14 of stem 9, chamber 4 and connection Al, as shown by the arrows on the accompanying drawing.

According to the illustrated embodiment of the invention, the air passage from the inside 14 of stem 9 to chamber 4 occurs through an annular lip seal or gasket 15, made of resilient material and fitted in a seat 16 formed in plug 17, the latter being inserted by screw threading 18 in the end portion 9a of the stem. The seal or gasket lip 1 5a adheres to the inner surface 9c of stem 9, so as to be separated from this surface when subjected to the pressure of vent air from chamber 12, but to sealingly adhere thereto when subjected below to the air pressure in the above mentioned chamber 4.

By such a behavour of seal or gasket 1 5, when said spring 8 is being compressed, the air in chamber 12 is allowed to vent to atmosphere through the annular passage 13, inside 14 of stem 9, threading 18 of plug 17, lip 1 spa, chamber 4 and connection Al.

On the other hand, when the vehicle driver operates the pedal distributor for duty braking, the incoming air in supply chamber 4 cannot reach said chamber 12, as this is precluded by said lip a 5a which, under these conditions, is pressure urged against the inner surface 9c of said stem and shuts off the passage.

Thus, by enabling an air vent through the cylinder interior, a device according to the invention avoids that, in case of aid or parking braking (bleed or vent of chamber 7 and stretching of spring 8), air from the outside and carrying any impurities, corrosion agents, etc.

therein contained may be sucked again in chamber 12, to the benefit of an improved conservation of the various members of the braking cylinder.

Claims

1. A vent device for pneumomechanical braking cylinders in vehicle braking systems and, particularly wherein the bleeding or venting to atmosphere of the housing chamber (12) for the spring (8) of the mechanical actuator (B) is effected through the inside (14) of the hollow stem (9) of said actuator and the supply chamber (4) of the pneumatic actuator (A), characterized by a unidirectional or one-way valve inserted within said hollow stem (9), communicating said housing chamber (12) for said spring (8) of said mechanical actuator (B) with said supply chamber (4) of said pneumatic actuator (A) as said spring is being compressed, while shutting off said communication during the supply of chamber (4) of said pneumatic actuator when duty braking is being operated.

2. A vent device according to Claim 1, characterized in that said unidirectional or oneway valve comprises an annular lip seal or gasket (15--15a) made of resilient material, and mounted within a seat (16) formed in a closure plug (17) of the end portion (9a) of said hollow stem (9), the lip (1 5a) of which cooperates with the inner surface (9c) of the stem for allowing the passage of vent air from the housing chamber (12) for said spring (8) of the mechanical actuator (B), while preciuding the reverse passage when subjected to the air presssure in suid supply chamber (4) of said pneumatic actuator (A).