GB2096259A - Load-responsive pressure- reduction in pneumatic brake systems - Google Patents

Abstract

A pneumatic tractor relay valve (as shown) or proportioning valve (fig 10, not shown) or a trailer relay valve (fig 12, not shown) includes a pressure proportioning device which comprises a plurality of concentric bushings (17) telescopically mounted in a chamber between a diaphragm control piston (15), and a coaxial reaction piston (19), pressure transmitted by means of said device depending on the number of said bushings, from the innermost outwards, which are engaging both the diaphragm and the reaction piston. The number of the bushings engaging both said diaphragm and said reaction piston varies inversely with the length of the stroke which said reaction piston has to travel to close the exhaust valve (36, 37) of reaction chamber (28), the exhaust valve having a seat (37) which is axially displaceable as the load acting upon the vehicle varies, moving towards the reaction piston, thereby to decrease said stroke length, as the load increases and away from said reaction piston, thereby to increase said stroke length as the load decreases, whereby the pressure transmitted through the bushings from the control or drive piston to the reaction piston increases as the load on the vehicle increases, and decreases as said load decreases. <IMAGE>

Description

SPECIFICATION A governor of the pneumatic braking pressure in the braking elements of a vehicle This invention relates to a novel type of governor for the pneumatic braking pressure in the braking elements of a vehicle.

The pressure governors normally used on vehicles comprise, as well known, two side-byside pistons, of which one is a control or drive piston actuated by compressed air during service or duty braking, and the other of which is a reaction piston subjected to the same pressure as that supplied to the braking elements to be controlled. A strain proportioning device comprising a rocking lever of varying fulcrum transmits the strain from the control or drive piston to the reaction piston in an amount depending on the load acting upon the vehicle, so that during braking wheel blocking is avoided when the load is null or minimum.

This varying fulcrum is implemented by means of a bearing sliding on the rocking lever, mounted at the free end of a rocking arm which, through a suitable linkage, is connected to the axis of the vehicle braking section to be controlled, while the governor is installed on the vehicle hanging portion or frame.

Such governors are mounted both on vehicles and on the trailers of vehicles. Mainly because of the provision of the rocking lever, rocking arm, and the said two side-by-side pistons, these pressure governors of the prior art are of quite complicated structure and cumbersome.

Accordingly, the overall size problems, as well as assembling difficulties, are increased if the governor is mounted on a vehicle trailer, as in such a case the governor should be connected either upstream or downstream of the emergency relay valve, that is the pneumetic apparatus which is normally provided on the trailer to obtain both the service or duty braking and the emergency braking of the latter.

It is an object of the present invention to provide a pressure governor in the braking elements of vehicles as a function of the load, which avoids the need for rocking members, such as the rocking lever, for the strain transmission.

In accordance with the present invention we provide a governor of the pneumatic braking pressure in the braking elements of a vehicle as a function of the load acting upon the vehicle, of the type including a control or drive piston actuated by compressed air during service or duty braking, a reaction piston defining a reaction chamber connected to the braking elements to be controlled, and a strain proportioning device which, during braking, transmits the strain from the control or drive piston to the reaction piston to a degree depending on the load acting upon the controlled portion of the vehicle, characterized in that said strain proportioning device comprises a plurality of concentric bushings telescopically mounted one within another in a chamber between the control or drive piston, which is of diaphragm type, and a coaxial piston comprising the reaction piston, the arrangement being such that the strain transmitted by means of said device depends on the number of said bushings, from the innermost outwards, which are engaging both the diaphragm and the reaction piston; and being further characterized in that the number of said bushings engaging both said diaphragm and said reaction piston is adapted to be varied inversely with the length of the stroke which said reaction piston has to travel to close the exhaust valve of said reaction chamber, said exhaust valve having a seat which is axially displaceable as the load acting upon the vehicle varies, moving towards the reaction piston, to thereby decrease said stroke length, as the load increases and away from said reaction piston, to thereby increase said stroke length, as the load decreases, whereby the strain transmitted through the bushings from the control or drive piston to the reaction piston increases as the load on the vehicle increases, and decreases as said load decreases.

By means of the present invention it becomes possible to provide a governor which is of relatively simple and compact structure.

According to a preferred embodiment of the invention, each bushing, except the innermost, has an inner annular seat and an outer annular seat, and the innermost bushing has an outer annular seat, the seats of the bushings being so arranged that the inner seat of each bushing cooperates with the outer seat of the adjacent inner bushing to axially stop the latter.

In accordance with one embodiment of the invention, the seat of the exhaust valve is provided at the inner end of the perforated push rod slidably sealingly traversing the end of the governor remote from the control or drive piston and terminating in the reaction chamber, and which is controlled from outside by a linkage connected to the appropriate axle of the vehicle, so as to effect axial displacements of the push rod tending to move the exhaust seat closer to or further away from the reaction piston, depending on whether the load on the vehicle increases or decreases, respectively.

According to an embodiment of the invention which is particularly suitable for a governor mounted on a towing vehicle, the operating piston having the bushings bearing thereon, and the reaction piston are rigidly interconnected to form a composite piston, the pistons defining therebetween a supply chamber communicating with the reaction chamber through an inlet valve, and retaining a movable valve element, in alignment with the push rod, which at an intermediate portion cooperates with the edge of a central opening of the reaction piston to provide said inlet valve, and having an end or extreme portion, extending into the reaction chamber, which cooperates with the inner end of the push rod to provide the exhaust valve, which movable valve element is subjected to the action of resilient means tending to move it to the closing position of the inlet valve.

Conversely, where the governor is to be mounted on a trailer so as to act also as an emergency relay valve, the composite piston may comprise a further piston or emergency piston of larger diameter than the other two pistons, defining two opposite annular chambers, both of which normally under pressure, a first chamber being in communication with said supply chamber, and the second chamber being connected to the direct duct (automatic duct) from the towing vehicle, and wherein said second chamber supplies the first chamber through a single-acting valve, so that under conditions of efficient pneumatic operation the composite piston is displaced by means of the control or drive piston, the effect of the equal and contrary or opposite pneumatic thrusts applied on the two opposite sides of the emergency piston being null, while under conditions of failure in the direct duct, the composite piston is displaced through the action of the pneumatic thrust on pressure air in the first annular chamber, to control the closing of the exhaust valve and opening of the inlet valve, and accordingly the emergency braking of the trailer.

Thus, this embodiment of the invention provides a pressure governor which also acts as an emergency relay valve, so that a single apparatus mounted on the trailer provides both the service or duty braking, with braking pressure adjusted in accordance with the load acting on the trailer, and the emergency braking of the latter.

Further features and advantages of the invention will become apparent from the foilowing description and accompanying drawings, referring, by way of example, to certain specific embodiments of the braking governor.

In the accompanying drawings: Figure 1 shows the diagram for a pneumatic braking system in a vehicle provided with a pressure governor according to a first embodiment of the invention; Figure 2 is a schematic longitudinal sectional view showing the pressure governor used in the system of Figure 1, under brake-released and partly loaded vehicle conditions; Figure 3 is a perspective view showing on a larger scale two sectioned elements of the strain proportioning device with which the pressure governor is provided; Figure 4 is a view showing the pressure governor of Figure 1 under the conditions of vehicle at full load and during service or duty braking; Figure 5 is a fragmentary enlarged view showing the configuration taken by the strain proportioning device of Figure 4 during braking;; Figure 6 is a view showing the pressure governor of Figure 1 under unloaded vehicle conditions during service or duty braking; Figure 7 is a fragmentary enlarged view showing the configuration taken by the strain proportioning device of Figure 6 during braking; Figure 8 is a cross-sectional view of the pressure governor shown in Figure 6, taken along line A-B; Figure 9 shows the diagram for a pneumatic braking system of a vehicle provided with pressure governor according to a second embodiment of the invention; Figure 10 is a schematic longitudinal sectional view showing the pressure governor used in the system shown in Figure 9, under brake-released and partly loaded vehicle conditions; Figure 11 is a diagram for a pneumatic braking system of a trailer provided with a pressure governor according to a third embodiment of the invention; and Figure 12 is a schematic longitudinal sectional view showing the pressure governor also acting as an emergency relay valve used in the system of Figure 11, under brake-released and partly loaded trailer conditions.

In the diagram of Figure 1, relating to a braking system suitable for a vehicle tractor, reference numeral 1 indicates the braking elements or cyclinders for the front axle, 2 indicates the braking elements or cyclinders for the rear axle, 3 indicates the compressed air distributor, and 4 indicates the pressure governor according to this embodiment of the invention. Two compressed air reservoirs Ka and K2 assure the system supply.

The governor 4 comprises a first inlet connection 5 connected to the distributor 3, a second inlet connection 6 connected to the reservoir K2, and an outlet connection 7 connected to the braking elements 2 which, in the case being examined, are the braking elements to be controlled.

As it will be hereinafter further explained, said governor uses the compressed air of reservoir K2, located adjacent thereto, to supply the braking elements 2. Therefore, the governor also acts as a response relay.

In order to obtain pressure regulation in said elements 2 as a function of the load acting on the corresponding axle, that is on the rear axle of the vehicle, the governor is mounted on the hanging portion or frame of the vehicle, and at its lower end has a push rod 8 capable of axially sealingly sliding therein under the control or command of an articulated linkage 9 which terminates at the rear axle 10 and which may be of any known type capable, as the load on the vehicle varies, of axially inwardly or outwardly moving said push rod 8 relative to the governor (see arrows) depending on whether the load on the axle increases or decreases.

In the arrangement illustrated, the above mentioned linkage comprises a lever 11 hinged at one end to a rocking arm 12 connected to said axle 10, and at the other end to an expansion or bracket 13 of the governor, while at an intermediate location said lever is connected to the push rod 8, so as to cause said axial displacements thereof, for the purposes to be hereinafter explained.

The pressure governor 4 is shown in detail in Figure 2 under the conditions of the vehicle being subjected to a general load and the brake being released, and in Figures 4 and 6 under the conditions of the vehicle at maximum load or nil load, respectively, during service or duty braking.

According to this embodiment of the invention, the control or drive piston 1 5 of the governor comprises a flexible diaphragm and transmits the strain to the reaction piston 16 through a plurality of concentric bushings 17, telescopically mounted in one another within a chamber 18, between said control or drive piston 1 5 and a coaxial composite piston 19 sealingly sliding in the governor body 20 and comprising the reaction piston 16.

The concentric bushings 1 7 form the strain proportioning device, which is operated by the control pressure supplied to the chamber 21 during braking through the inlet connection 5.

As more clearly shown in Figure 3, each bushing 1 7 (except the innermost bushing) is formed of two stepped cylindrical parts, of which the upper part is of larger diameter, so that each of the bushings has an inner annular seat S, and an outer annular seat S2 at a lower level. The innermost bushing 1 7i has an outer seat but no inner seat.

The seats St and S20f each bushing are at a higher level than the similar seats of the adjacent outer bushing, and also the inner seat S, of a bushing and the outer seat S20f the adjacent inner bushing are in axial alignment and normally spaced apart so that, during operation, the inner seat S, of any bushing cooperates with the outer seat S20f the adjacent inner bushing for axially stopping the latter, or converseiy the outer seat S2 cooperates with the inner seat S, of the adjacent outer bushing to stop there against.

The outer seat S20f the outermost bushing 1 7e (Figs. 2, 4 and 6) cooperates with a fixed seat S presented by the governor body 20. As mentioned, the innermost bushing 17i has no inner seat. Instead, at the control side it has a bottom wall 1 7a so as to provide a larger bearing surface to the diaphragm piston 1 5.

The composite piston 19 comprises two pistons of the same diameter, namely an operating piston 22 having said bushings 1 7 acting thereon, and the above mentioned piston 1 6. Therebetween the two pistons define, with a perforated cylindrical wall 23 rigidly connecting the two pistons, an inner supply chamber 24 communicating through passages 25, annular chamber C and passage 26 with the connection 6 connected to the reservoir K 2 The piston 1 6 and the lower end 27 of the governor define the reaction or response chamber 28, which is connected through the connection 7 to the braking elements 2.

The operating piston 22 extends inwardly of the supply chamber 24 with the tubular extension 29 which receives and sealingly guides one end of a movable valve element 30, the other end of which passes through a central opening 31 of the reaction piston 1 6 and terminates in the reaction chamber 28. At an intermediate position, this element 30 carries an anchored seal 32, which cooperates with a seat presented by the edge 33 of said opening, to provide the inlet valve 32, 33 connecting the supply chamber 24 with the reaction chamber 28.

This last mentioned valve is normally closed by the action of a spring 34 mounted between the lower end of said extension 29 and an inner abutment 30i of the movable element 30, which is perforated.

The element 30 also has an annular shoulder 35 intended to abut either against the piston 16 or a part thereof, as shown, or against the end of the tubular extension 29. Thus, the element 30 is retained to the two pistons 22, 1 6, relative to which it can be moved only by limited axial displacements.

The end of element 30 terminating in the reaction chamber 28 has a head 36 which forms the seal of the normally open exhaust valve, the seat 37 of which is carried by the movable push rod 8 in alignment with said element 30.

The push rod has a bore 38 for the bleed to atmosphere of the air in chamber 28.

As above mentioned, the push rod 8 axially sealingly slides in the lower end 27 of the governor under the control of the linkage 9, so as to move the seat 37 towards seal 36 as the load on the vehicle increases, and conversely to move it away as the load decreases.

The operation of the pressure governor will now be discussed with reference to Figs. 1 to 7, wherein the corresponding parts are designated by the same references.

Partly loaded, but brake-released vehicle The position taken by the various parts of the governor under these conditions is shown in Fig.

2. It will be seen that the inlet valve 32, 33 is closed, while the exhaust valve 36, 37 is open.

The supply chamber 24 is under pressure, being directly connected through the openings 25, annular chamber C, opening 26 and connection 6 to the reservoir K2.

The control chamber 21 and reaction chamber 28 are connected to atmosphere through the distributor 3 and through the bore 38 of the push rod, respectively.

Under these conditions, the bushings 1 7 are completely overlapped and at one side are all in contact with the diaphragm piston 15, and at the other side with the operating piston 22. The inner and outer seats S,, S20f bushings are opposite and distant, such seats cooperating with one another.

The perforated push rod 8 and accordingly the seat 37 of the exhaust valve, take an intermediate axial position corresponding to the partial load acting upon the vehicle. Therefore, from this position, by varying the load said push rod is allowed to move in either direction, as shown by the arrows. Reference L indicates the general distance between an outer shoulder 8a of the push rod and an outer abutment 27a of the governor bottom 27, corresponding to said partial load.

Vehicle with maximum load during service or duty braking The position taken by the various parts under these conditions is shown in Figs. 4 and 5.

At maximum load, the push rod 8 completely penetrates into the reaction chamber 28, whereby the distance between the shoulder 8a and abutment 27a is nil (L=O).

Obviously, the seat 37 of the exhaust valve takes the closest axial position relative to the reaction piston 1 6. As a result, during braking, upon supply of the control chamber 21 by operation of the distributor 3, there will occur a minimum displacement of the composite piston 19, as well as of the reaction piston 16, for the closing of said valve.

After the closing of the exhaust valve 36,37, the inlet valve 32, 33 opens and compressed air from supply chamber 24 passes to the reaction chamber 28, and therefrom through the connection 7 to the braking elements 2 to control the vehicle braking.

Due to the minimum displacement of the composite piston 19, all of the bushings 1 7 are still in contact with both the diaphragm 1 5 and operating piston 22. The maximum strain is transmitted, since the operative or control surface of the diaphragm, defined by the diameter of the outermost bushing 17e, is the maximum.

Air from above to said chamber 28 is also effective on the reaction piston 1 6 with a force which is in opposition to the control or drive force transmitted to said piston through the bushings 17, and the value of which depends on the air pressure in chamber 28. As air arrives thereat, there is a corresponding increase in pressure, until the reaction force on the piston 1 6 equalizes the control or drive force, causing the upward displacement of the piston 1 6 and accordingly the closing of the inlet valve, while the exhaust valve 36 remains closed.

In this case, such a situation occurs when the reaction pressure in chamber 28 reaches the value of the control or drive pressure in chamber 21, being the control surface of the diaphragm 1 5 and the reaction surface of piston 1 6 equal.

By increasing the control or drive pressure in said chamber 21, the piston 16 is further downwardly urged, causing the reopening of the inlet valve 32, 33. Then, additional air arrives at the chamber 28 with resulting increase in pressure until reaching the new value of the control or drive pressure, at which point the piston 1 6 moves upwardly again and closes the inlet valve.

Thus, during braking, as the control or drive pressure increases, the exhaust valve 36, 37 remains closed, and the piston 1 6 continuously moves downwardly and upwardly, opening and closing the inet valve until a balance condition is reached, which occurs when the control or drive pressure remains constant and the reaction pressure reaches the same value.

During braking, only the outer seat S20f the outermost bushing 1 7e abuts on the respective seat S of the body S, the other cooperating seats S, and S2 remaining spaced apart from one another.

From the foregoing, it will be seen that the maximum control strain transmitted to the reaction piston 16 has a pressure in chamber 28 corresponding thereto, the latter being also at the maximum rate since it is equal to the control or drive pressure. Therefore, under the conditions of maximum load on the vehicle, the governor provides for supplying to said chamber 28, as well as to the braking elements 2, a braking pressure which is at maximum value and thus proportioned to the load.

During braking, air in chamber 21 bleeds to atmosphere through the distributor 3 and the composite piston 19, which is no longer subjected to the control strain, is upwardly urged to take again the rest or inoperative position, thus closing the inlet valve and opening the exhaust valve.

Thus, air in said braking elements 2 and chamber 28 is allowed to bleed to atmosphere through the bore 38 of said push rod 8.

Vehicle with no load during service or duty braking The position taken by the various parts under these conditions is shown in Figs. 6 and 7.

Owing to null load, the push rod 8 is in the least inserted position in the reaction chamber 28, so that the distance between the shoulder 8a and abutment 27a is maximum and indicated by L max. Obviously, the seat 37 of the exhaust valve 36, 37 takes the farthermost axial position from the reaction piston 16, whereby on braking, the stroke that this piston has to travel to provide for closing said exhaust valve is at its maximum.

At the end of such a stroke, the diaphragm 15 is deformed to the maximum extent, and the bushings 1 7 take the telescopical configuration shown in Figs. 6 and 7. Particularly, it will be seen in Fig. 7 that each bushing, from the outermost one inward, will seat by its own outer seat S2 on the inner seat S, of the adjacent outer bushing. In order, the first bushing coming to a stop is the outermost bushing 17e, which abuts on the fixed seat S.

Thus, the only bushing engaging both said diaphragm 1 5 and operating piston 22 is the innermost bushing 17i. As a result, the strain transmitted to the reaction piston 1 6 is at a minimum, as the operative surface of the diaphragm 15, which is defined by the diameter of the smallest bushing 17i, is at its minimum.

Accordingly, the pressure in chamber 28 capable of developing a reaction force on piston 1 6 to equalize the control or drive pressure will always be lower than the control or drive pressure in chamber 21. Particularly, since the control or drive pressure is at a minimum, correspondingly, the pressure that can be provided in chamber 28 will be the minimum, and accordingly in the braking elements 2.

Thus, under said conditions of null load on the vehicle, the governor provides for supplying to said elements 2 a minimum braking pressure, which is proportioned to the load.

Partially loaded vehicle during service or duty braking Under these conditions, the push rod 8 will take an intermediate axial position depending on the load acting on the vehicle, for example the position shown in Fig. 2.

Accordingly, during braking the bushings also will take an intermediate telescopical configuration between that under full load shown in Fig. 4 and that under null load shown in Fig. 6.

This means that only some of the bushings 17, apart from the innermost bushing, will transmit the strain from said diaphragm 15 to piston 16, and the value of this strain is determined by the diameter of the outermost bushing among those cooperating with the strain transmission.

As will be apparent, the intermediate control strain applied to the piston 16 will cause a corresponding braking presure in said chamber 28, as well as in the braking elements 2, and these will be of intermediate in value between the maximum and minimum values.

A second embodiment of a governor in accordance with this invention is shown in Figs. 9 and 10, and is applicable if the braking elements 2 are supplied through the distributor 3.

In Figures 9 and 10, parts corresponding to parts in Figs. 1-8 are designated by the same references.

The governor shown in Fig. 10 differs from that above described in connection with Figs. 1-8 in that the supply chamber 24 is connected through the distributor 3 to a reservoir K3, and in that the inlet valve 32, 33 is normally open, whereas the exhaust valve 36, 37 is normally closed.

To this end, the governor has only two connections 5 and 7, the first of which in addition to communicating with the control chamber 21 also communicates with the supply chamber 24 through the annular chamber C formed between the body 20 and wall 23 and the openings 25 provided in the latter.

Furthermore, a preloaded spring 39 mounted between the piston 22 and wall 1 7a of the innermost bushing 17idownwardly urges the composite piston 19, so that the governor parts take the position shown in Fig. 10, which corresponds to the rest or inoperative position of the apparatus and with partially loaded vehicle.

The above described considerations regarding the position of said push rod 8 as a function of the load and control or drive strain transmitted through the bushings to the piston 16, are also true for this embodiment of the governor.

In this embodiment also, the stroke that the piston has to travel from the uppermost position to provide for closing the exhaust valve 36, 37 will vary inversely to the load on the vehicle.

The operation of the governor is also the same as that described for the governor illustrated in Figs. 1-8, with the only difference being that the compressed air arriving at the control chamber 21 simultaneously arrives at the reaction chamber 28, the inlet valve 32, 33 being open. Then, as the pressure in said chamber 28 increases, the piston 1 6 is upwardly moved to close the inlet valve and then downwards to reopen the valve as the control or drive pressure in chamber 21 increases, and so on.

During brake release, the air bleeds to atmosphere through the distributor 3 and the bore 38 of the push rod 8.

A third embodiment of the governor in accordance with this invention, suitable for a vehicle trailer, is shown in Figs. 11 and 12. In this embodiment, the apparatus is mounted on the trailer and provides for governing the pressure in the braking elements of the latter as a function of the load acting thereon. In this case the linkage 9 is connected to an axle of the trailer. The parts corresponding to the governor shown in Figs. 1- 8 are designated by the same references.

The governor shown in Fig. 1 2 differs from that shown in Fig. 2 in that the composite piston 19' comprises a further or emergency piston 40 located between the operating piston 22 and reaction piston 16, but of larger diameter.

Moreover, as shown in Fig.11, the governor has four connections 41, 42, 43 and 44, the first and second of which are connected through the coupling 45 respectively to the service or duty duct and direct duct from the towing vehicle e.g. a tractor, the third 43 of which is directly connected to a reservoir K4 of the trailer, and the fourth 44 of which is connected to the braking elements 46 of the trailer. As well known, the service or duty duct, commonly referred to as governable duct, is put under pressure during service or duty braking, while the direct duct, commonly referred to as automatic duct, is normally under pressure and supplies the trailer reservoir K4.By means of a unidirectional gasket 47, the emergency piston slides in the governor body 20' and defines two opposite annular chambers C, and C2 provided between said body 20' and wail 23 of the composite piston 19'. Both of said chambers are normally under pressure, and to this end chamber C1 communicates through the passages 25, supply chamber 24 and connection 43 with said reservoir Ka, whereas chamber C2 communicates through the passage 48 and conection 42 with the direct duct. The gasket 47 allows the air passage from chamber C1, but not vice-versa.

The provision of the third piston 40 does not affect the operation of the governor under the conditions of efficient braking circuits. Thus, under such conditions, this piston 40 is subjected to a null pneumatic thrust, the pneumatic forces acting on the two opposite sides being equal and opposed. Therefore, during service or duty braking, said governor behaves as the governor of Fig. 2 under the various load conditions.

On the other hand, upon breakage of the direct duct connected to the connection 42, chamber C2 is exhausted to atmosphere, and accordingly said piston 40, being subjected to only the pneumatic thrust of air in the opposite chamber C1, moves downwards drawing along the composite piston 19' which causes the closing of the exhaust valve 36, 37 and then the opening of the inlet valve 32, 33. Thus, said chamber 28 as well as the braking elements 46 are supplied from the reservoir K4 through the chamber 24 and said valve 32, 33, thereby assuring the emergency braking of the trailer.

Therefore, in addition to operating as pressure governor in the elements 46 to provide a service or duty braking proportional to the load acting on the trailer, such a governor also operates as emergency relay valve for providing the emergency braking.

Thus, it will be apparent that there are advantages of economy and in overall size reduction in using the governor shown in Fig. 12, instead of two distinct devices (governor and emergency relay valve) such as are normally mounted on the trailer to obtain the same results.

However, it will also be apparent that, if desired, a pressure governor of this invention, such as that shown in Fig. 2, can be installed on the trailer as a distinct apparatus, that is separated from the emergency relay valve. In this case, the governor may be inserted in the braking circuit of the trailer either upstream or downstream of the emergency relaya valve.

Should the governor shown in Fig. 2 be inserted downstream of the emergency relay valve.

the connection 5 would be connected to the outlet of said emergency relay valve, the connection 6 would be connected to a reservoir of the trailer, and the connection 7 would be connected to the braking elements of the latter.

On the other hand, should the governor be mounted upstream of the emergency relay valve, then the connection 5 would be connected to the duty or service duct (or governable duct) from the tractor, the connection 6 would be connected to a reservoir of the trailer, and the connection 7 to the service or control inlet of the emergency relay valve. Also, if desired, the governor of Fig. 10 can be installed on the trailer as an independent apparatus. When inserted downstream of the emergency relay valve, then the connection 5 of said governor of Fig. 10 is connected to the output of the emergency relay valve, and the connection 7 is connected to the braking elements.

On the other hand, when inserted upstream, the connection 5 is connected to the service or duty duct (or governable duct) from the tractor, and the connection 7 is connected with the duty or service input of the emergency relay valve. The operation of the governor on the trailer is just as that described above for Figs. 2 and 10. Similarly, during service or duty braking, all of bushings under the condition of full load of the trailer, participate in strain transmission from the control or drive piston to the reaction piston, whilst only the innermost bushing participates in strain transmission under the condition of unloaded trailer, and in the intermediate case of a partly loaded trailer a number of bushings, from the innermost bushing outwards, participate in such transmission.

In accordance with an optional feature of the invention, applicable to the governors of Figs. 2 and 12, the connection 5 or 41 is connected with the chamber 18, having the bushings 17 housed therein, through a pressure reducing valve.

This connection has the purpose of obtaining, at a first stage of the service or duty braking, a fast initial supply to the braking elements which, under any load condition of the vehicle, will assure the approach of the brakes shoes to the drums. The pressure reducing valve, which may be of any known type, is inserted in the governor body or casing,as shown in Fig. 8. It comprises a piston 49 subjected at one side to the action of a preloaded spring 50.

The piston carries a seal 51 cooperating with a valve seat 52. Due to the spring, such a valve 51, 52 is normally open, so that In addition to communicating with the control chamber 21 the connection 5 or 41 also communicates through the passage 53, the chamber 54 of the reducing unit, the open valve 51, 52 and the hole 55 with the chamber 18.

The load or force of said spring 50 can be adjusted by operation of a screw 56.

During service or duty braking, compressed air also arrives at the chamber 18, but as soon as the pressure in chamber 54 of the reducing unit reaches the predetermined reduced value by the load or force of spring 50, the piston 49 is urged towards said spring and closes the valve 51, 52.

At this supply step, the pressure in chamber 18 causes the displacement of the composite piston 1 9 or 19' of the governor, with resulting opening of the inlet valve 32, 33 and supply to the braking elements 2 or 46. Thus, at the initial braking step, the composite piston is operated independently of the control pressure in chamber 21, whereby the pressure in chamber 28 and braking elements will rapidly increase, assuring under any load condition of the vehicle the approach of the shoes to the drums.

Thereafter, it is the diaphragm 1 5 that through the bushings transmits the strain to the piston 1 9 or 19'. But, during this following step, the pressure in the reaction chamber 28 increases by the same law as the pressure in chamber 21, and accordingly the trailer braking continues as a function of the control or drive pressure.

Claims (11)

Claims

1. A governor of the pneumatic braking pressure in the braking elements of a vehicle as a function of the load acting upon the vehicle, of the type including a control or drive piston actuated by compressed air during service or duty braking, a reaction piston defining a reaction chamber connected to the braking elements to be controlled, and a strain proportioning device which, during braking, transmits the strain from the control or drive piston to the reaction piston to a degree depending on the load acting upon the controlled portion of the vehicle, characterized in that said strain proportioning device comprises a plurality of concentric bushings telescopically mounted one within another in a chamber between the control or drive piston, which is of diaphragm type, and a coaxial piston comprising the reaction piston, the arrangement being such that the strain transmitted by means of said device depends on the number of said bushings, from the innermost outwards, which are engaging both the diaphragm and the reaction piston; and being further characterized in that the number of said bushings engaging both said diaphragm and said reaction piston is adapted to be varied inversely with the length of the stroke which said reaction piston has to travel to close the exhaust valve of said reaction chamber, said exhaust valve having a seat which is axially displaceable as the load acting upon the vehicle varies, moving towards the reaction piston, as to thereby decrease said stroke length, as the load increases and away from said reaction piston, to thereby increase said stroke length, as the load decreases, whereby the strain transmitted through the bushings from the control or drive piston to the reaction piston increases as the load on the vehicle increases, and decreases as said load decreases.

2. A pressure governor according to Claim 1, characterized in that each of said bushing, except the innermost bushing, has an inner annular seat and an outer annular seat at a level relative to said inner seat further from said drive piston which seats of each bushing are at a level closer to said drive piston than the similar seats of the adjacent outer bushing, the innermost bushing having an outer annular seat, whereby the inner seat of each bushing will cooperate with the outer seat of the adjacent inner bushing for limiting axial movement of the latter bushing.

3. A pressure governor according to Claim 2, characterized in that the innermost bushing has an end wall against which the control or drive piston acts.

4. A pressure governor according to any preceding claim, characterized in that said seat of the exhaust valve is provided at the inner end of a perforated push rod axially passing through the end of the governor remote from said control or drive piston and terminating in the reaction chamber, and sealingly sliding in said reaction chamber under control of a linkage for connecting said outer end of said push rod to the axle of the vehicle, whereby the axial displacements of the push rod will cause the exhaust seat to move near or away from the reaction piston depending on whether the load on the vehicle increases or decreases, respectively.

5. A pressure governor according to Claim 4, characterized in that the operating and reaction pistons are fixedly interconnected to form a composite piston and define therebetween a supply chamber which communicates through an inlet valve with the reaction chamber, said pistons retaining a movablle valve element in alignment with the push rod, which valve element at an intermediate portion cooperates with the edge of a control opening of the reaction piston to provide the inlet valve, and having an end portion extending in the reaction chamber which cooperates with the inner end of the push rod to provide the exhaust valve, the valve element being subjected to the action of resilient means tending to move it to the closing position of the inlet valve.

6. A pressure governor according to Claim 5, characterized in that the operating piston has a tubular extension inside the supply chamber for receiving and sealingly guiding the end of the movable element opposite to that cooperating with the push rod to form the exhaust valve; the displacements of the movable element relative to the composite piston occurring between the end of the tubular extension and the reaction piston, to which said element is urged through the action of said resilient means which at the other end bear on the tubular extension.

7. A pressure governor according to any preceding claim, characterized in that the inlet valve is normally closed and the exhaust valve is normally open, and in that the supply chamber is adapted to be directly connected to a compressed air reservoir of the vehicle, so as to be permanently under pressure, while the operating chamber of the control or drive piston is adapted to be connected to a source of compressed air during service or duty braking.

8. A pressure governor according to any one of Claims 1 to 6, characterized in that the inlet valve is normally open and the exhaust valve is normally closed through the action of resilient means mounted in the chamber housing the bushings, between the control or drive piston and the operating piston, and in that the supply chamber and the operating chamber of the control or drive piston are adapted to be simultaneously connected to a compressed air source during service or duty braking.

9. A pressure governor according to any one of Claims 5-7, for installation on a vehicle trailer, and being adapted to act also as an emergency relay valve, characterized in that the supply chamber is adapted to be directly connected to the trailer reservoir and the operating chamber of the control or drive piston is adapted to be connected to the service or duty duct (governable duct) from the towing vehicle in that the composite piston further comprises a third piston or emergency piston of a larger diameter than the other two pistons, to which it is rigidly connected, defining two opposite annular chambers, both of which are under pressure in operation, a first chamber communicating with said supply chamber and trailer reservoir, and the second chamber being adapted to be connected to the direct duct (automatic duct) from the towing vehicle, and in that said second chamber supplies the first chamber through a unidirectional valve, whereby under efficient pneumatic conditions of the braking system the composite piston moves by the action of the control or drive piston, the effect of the equal and opposed pneumatic thrusts being null, applied to the two opposite sides of the emergency piston, while under conditions of failure in the direct duct the composite piston moves through the action of the pneumatic thrust of pressure air in the first annular chamber, to control the closing of the exhaust valve and the opening of the inlet valve, and accordingly the emergency braking of the trailer.

1 0. A pressure governor according to any one of Claims 5-7 or 9, characterized in that during the service or duty braking said housing chamber for the bushings is adapted to be supplied through a pressure reducing valve from the same compressed air source supplying the operating chamber of the control or drive piston, so that during said braking the composite piston initially moves through the action of the pneumatic pressure of reduced value set by said reducing unit, and thereafter through the action of the pneumatic control pressure acting on the control or drive piston, thus allowing the response pressure in the reaction chamber to rapidly increase at the start of braking, being unaffected by the control pressure, and thereafter to increase with said control pressure.

11. A pressure governor according to Claim 10, characterized in that the pressure reducing valve is formed in the governor body or casing between the service supply inlet and the chamber housing the bushings.

1 2. A pressure governor substantially as hereinbefore described with reference to Figs.

1-8, Figs. 9 and 10 or Figs. 11 and t2 or the accompanying drawings.

1 3. A vehicle or vehicle trailer having a braking system which includes a pressure governor according to any preceding claim.