GB2076915A - A double control servo-distributor for pneumatic braking systems in vehicles - Google Patents

Abstract

The invention relates to a double control servo-distributor for pneumatic braking systems in vehicles, comprising a main piston (17) for the control of the inlet valve (12) of the braking cylinders and an emergency piston (18) for the operation of the main piston in case of feed failure in the latter. The emergency piston has a push rod (30) sealingly sliding within a seat (31) of the main piston (17), so that the pneumatic thrust or pressure acting on the emergency piston (18) at the inlet side (at 41) is larger than that applied to the opposite surface (at 39 and 40). Thus, a displacement of the emergency piston is also provided under conditions of full efficiency of the supply circuits (6, 7) and the jamming of the emergency piston in the cylinder due to sticking of its gaskets or packings against the walls of the latter is avoided. <IMAGE>

Description

SPECIFICATION A double control servo-distributor for pneumatic braking systems in vehicles This invention relates to a double control servodistributor for pneumatic braking systems in vehicles, of the type wherein the double control is provided by means of two pistons normally sliding within a same cylinder and placed one after the other (in tandem), one of which or the main piston for the control of the inlet valve of the involved braking cylinders, and the other or emergency piston for the operation of the main piston in case of feed failure, having a stem provided with an axial passage for the feed and exhaust for the operation chamber of the main piston.

As well known, in servo-distributors of this type, the operation chambers for the two pistons are supplied by two distinct pneumatic circuits activated through a pedal distributor.

Under efficiency conditions for both of these circuits, during service braking controlled by means of said distributor, only the main piston is moved operating the control valve for the feed of the involved braking elements, while the emergency piston remains still at rest position, as subjected on the two faces to two equal and contrary pneumatic thrusts or pressures, the opposite surfaces exposed to pressure being equal.

The holding at stationary position for the emergency piston under said efficiency conditions of the circuits may lead to its jamming against the cylinder walls due to adhesion or glueing or sticking of its gaskets or packings on said walls, with the result that, in case of failure in the feed circuit for the operation chamber of the main piston, said emergency piston during braking, while being subjected to the air pressure in its operation chamber, is prevented from moving and accordingly acting upon the main piston for the valve control. Therefore, there is the risk with known distributors that in case of failure to said feed circuit during the vehicle braking, the involved braking cylinders are not supplied, and finally, that no braking would occur to that axle of the vehicle, normally the rear axle, controlled by the servo-distributor.

It is the object of the present invention to provide a double control servo-distributor of the above described type, overcoming the above mentioned disadvantage so that its operation is assured in case of breakage or failure in the feed circuit for the operation chamber of the main piston.

Accordingly, the technical problem to be solved is to provide a servo-distributor of the above mentioned type, in which the emergency piston would be moved or displaced also during normal operation of the two pneumatic circuits, so as to avoid any glueing or sticking of its gaskets or packings against the cylinder walls.

According to the invention, such a technical problem has been solved by means of a servodistributor characterized in that the emergency piston at that side facing the main piston has a push rod sealingly sliding within a seat provided by the main piston and that the axial passage of the emergency piston stem is a blind passage and communicates by means of a side passage in said emergency piston with the operation chamber of the main piston, so that the surface of the latter facing the main piston and exposed to pressure is less than the opposite surface also exposed to pressure.

By means of said embodiment, the result is obtained that during braking the pneumatic thrust or pressure acting on the emergency piston at the inlet side is greater than the thrust or pressure, of contrary sign, applied to the opposite surface facing the main piston, and accordingly the emergency piston will move substantially in synchronism with the main piston, whenever the braking is controlled both with efficient and failed or broken pneumatic circuits.

The following description given by way of mere unrestrictive example of the present invention is referred to the accompanying drawings, in which: Figure 1 is a scheme showing the pneumatic braking system for a vehicle provided with a servodistributor according to the present invention; and Figure 2 is a schematic vertical sectional view showing one embodiment of the servo-distributor according to the invention.

The scheme of Figure 1 shows a pneumatic braking system for a two-axle vehicle, in which a double control servo-distributor S is inserted. Reference numerals 1 and 2 respectively denote the braking cylinders (or elements) for the front and rear wheels of the vehicle, which are supplied with compressed air from tanks 3 and 4 under operation of the pedal distributor 5 during service braking.

The feed of cylinders 1 conventionally occurs through distributor 5, while the feed of cylinders 2 occurs through servo-distributor S when controlled by two distinct pneumatic circuits 6 and 7, in turn controlled by said distributor. To this end, said servo-distributor S has four connectors, of which two connectors 8 and 9 are respectively connected to circuits 6 and 7, and of which two connectors 10 and 11 are respectively connected to tank 4 and cylinders 2.

Upon operation of distributor 5, said servodistributor S controls the opening of a valve 12 (see Figure 2) which communicates said connector 10 with said connector 11. Thus the braking is provided for the rear wheels controlled by cylinders 2, in addition to that for the front wheels controlled by cylinders 1. Upon release of the pedal of said distributor 5, the air of the braking cylinders 2 is vented to atmosphere through the hole 13 of the servo-distributor, whereas the air of the pneumatic circuits 6 and 7 and cylinders 1 is vented to atmosphere through said distributor 5.

The invention is concerned with a particular embodiment of the double control servo-distributor S.

Such a servo-distributor is schematically shown in sectional view in Figure 2, in which reference numeral 14 denotes the body of the apparatus and 15 and 16 two inner walls, between which two pistons are arranged, of which one piston 17 is the main piston, and the other piston 18 is the emergen cy piston, both of which providing the double control. Reference numeral 19 denotes the operation chamber for the main piston and 20 denotes the operation chamber for the emergency piston. By means of a push rod 21 said main piston 17 controls the normally closed valve 12, which is provided with a hole 22 in communication with the exhaust hole 13 in the bottom ofthe apparatus.

Said emergency piston 18 has at the inlet side a stem 23 sealingly sliding within a sleeve 24, defining together with wall 15 at the top two chambers 25 and 26.

At braking step, the opertion chamber 19 for the main piston 17 is supplied by circuit 6 through said connector 8, chamber 25, an opening 27 in said sleeve 24 and an axial passage 28 provided internally of said stem 23.

During braking, the operation chamber 20 for the emergency piston 18 is supplied by circuit 7 through said connector 9, chamber 26 and an opening 29 in said wall 15.

In accordance with the present invention, on the side facing the main piston 17 said emergency piston has a push rod 30 sealingly sliding within a seat 31 provided by the main piston 17 andthatthe axial passage 28 of stem 23 is a blind passage and communicates through a side passage 32 in emergency piston 18 with said chamber 19.

In a simple embodiment, said guide seat 31 for push rod 30 is provided by means of a through hole 33 in the main piston 17, whereas sealing is ensured by a simple gasket or packing 34. Should both of said circuits 6 and 7 be efficient, air arrives during braking both at said connector 8 and at said connector 9 and accordingly to said operation chambers 19 and 20, respectively, of the two pistons 17 and 18. Under these conditions, said emergency-piston 18 is urged in downward direction and substantially in synchronism also said main piston 17 is moved and opens said valve 12 retained by means of a spring 36 on a seat 35 provided by said wall 16. Thus, the compressed air passes from chamber 37 communicating with connector 10 to chamber 38 communicating with connector 11, and therefrom to the braking cylinders 2 for braking.Upon release of braking, said chambers 19 and 20 are vented to atmosphere through distributor 5 and chamber 38 through the exhaust holes 22 and 13, while the parts resume the positions shown in Figure 2. Particularly, said pistons 17 and 18 resume the rest position due to the thrust acting on said piston 17 from the-air in chamber 38 being vented.

Under said conditions of full efficiency of the two pneumatic circuits, said emergency piston 18 is displaced because of being subjected at the inlet side to a pneumatic thrust or pressure larger than the contrary thrust or pressure acting on the opposite surface, that is that surface facing said main piston 17. This difference in thrust or pressure is due to the difference between the two surfaces subjected to pressure, the pressures of the two circuits being the same. Thus, the surface of emergency piston 18 subjected to pressure at the inlet side, and which is given by the sum of surface 39 with the front surface 40 of stem 23, is largerthan the opposite annular surface 41, which has been just reduced by the full section of push rod 30.In the case where the pneumatic circuit 6 is in failure and the pneumatic circuit 7 is instead efficient, during braking only the chamber 20 of the emergency piston 18 is supplied, sa that this last mentioned piston is still downward displaced and carries along the main piston 17 controlling the valve 12.

Thus, by the expedient according to the invention, of the provision of a push rod 30 sealingly sliding within the seat 31, during braking said emergency piston 18 always moves either with said pneumatic circuits 6 and 7 efficient, or with the pneumatic circuit 6 in failure, which is advantageous since said emergency piston 18 can operate on said main piston 17 should a breakage or failure occur in said circuit 6, that is to say the main feed circuit.Due to engagement of push rod 30 with seat 31, should efficiency conditions persist for both of said circuits 6 and 7, the drawback could occur that said push rod would become jammed to said main piston 17 by glueing or sticking of its gasket or packing 34 in said seat 31 This jamming (which could arise due to the relative lack of motion between the two pistons 17 and 18) would not allow the servo-distributorto be effective in case of breakage or failure of circuit 7 since the air arriving only at chamber 19 would not cause any displacement of the integral assembly of said pistons 17 and 18.

In order to minimisethe riskofthis possibility, the inner feed circuit connecting said connector 8 with chamber 19 has, according to the illustrated embodi mentofthe invention a gauged passage of a narrow size relative to opening 29, through which said chamber 20 is supplied. In the solution shown, this gauged passage is provided by means of the side passage 32 in said emergency piston 18 and con necks the inside 28 of stem 23 with said chamber 19.

By such an expedient the condition is met that upon brake release first said chamber 20 is vented through the wide opening 29, and then said chamber 19 is vented through the narrow passage 32.

Thus, an-advance is obtained for the return movementto rest position of emergency piston 18 relative to the similar movement of main piston 17, achieving a relative movement of the two pistons at each braking release, which helps to avoid the sticking or adhesion of said gasket or packing 34 in said seat 31.

Reference was made to a push rod 30 sealingly sliding within a seat 31 made with a through hole 33 in said main piston 17. However, the role of the parts could be inverted. Thus, the engagement could occur between an inner central push rod of main piston 17 and a guide seat presented by the emergency piston 18, the latter provided by a tubular sleeve on the extension of stem 23, investing and sealingly sliding on the push rod of main piston 17, the axial passage 28 of stem 23 being still a blind massage and in communication with said chamber 19.

Furthermore, the invention has been described with reference to a servo-distributor operating as a speed relay, that is as a repeater apparatus capable of accelerating the control response speed.

However, it will be apparent that the invention is also applicable to a servo-distributor used as a protective valve against overstresses acting on the braking members in systems with pneumatic/ mechanical type of braking cylinders.

In this use, it is known that the main piston of the servo-distributor holds the valve at normally open condition, its operation chamber being normally kept under pressure through a manual distributor, whereas the operation chamber of the emergency piston is supplied during operation of the pedal distributor.

Claims (4)

1. A double control servo-distributor for pneumatic braking systems in vehicles, of the type wherein the double control is provided by means of two pistons normally sliding within a same cylinder and arranged one after the other (in tandem), one of which or the main piston for the control of the inlet valve of the involved braking cylinders, and the other or emergency piston for the operation of the main piston in case of feed failure, having a stem provided with an axial passage for the feed and exhaust for the operation chamber of the main piston, characterized in that the emergency piston (18) at the side facing the main piston (17) has a push rod (30) sealingly sliding within a seat (31) in the main piston, and that the axial passage (28) of the stem (23) of the emergency piston is a blind passage and communicates with the operation chamber (19) of the main piston by means of a side passage (32) provided in said emergency piston, so that the surface (41) facing the main piston and exposed to pressure is less than the surface (39,40) of the opposite face also exposed to pressure.

2. A servo-distributor according to Claim 1, characterized in that the sliding seat for the push rod comprises a through hole (33) in the main piston (17).

3. A servo-distributor according to Claim 1, characterized in that the inner feed circuit for the operation chamber (19) ofthe main piston (17) has a gauged passage which is narrow relative to the supply passage for the operation chamber (20) of the emergency piston (18), so that the exhaust of the operation chamber (20) of the latter occurs prior to the exhaust of the operation chamber (19) of the main piston.

4. A servo-distributor according to Claim 3, characterized in that said narrow gauged passage is provided by the side passage (32) in said emergency piston.