GB2086511A - A load-responsive pneumatic pressure proportioning device for vehicle braking systems in braking - Google Patents

Abstract

Undesirable operation of a pneumatic pressure proportioning device e.g. on rough roads at full vehicle load is prevented. The pneumatic proportion device includes a variable fulcrum rocker arm 6 for proportioning the braking pressure in the braking elements in response to the load acting on the vehicle, and a swinging arm 15 responsive to said load the arm having a bearing 14 at its free end to provide for varying the fulcrum position. At the position taken by the fulcrum under the condition of full load of the vehicle, the rocker arm 6 has a roller 19, and, at the free end, in addition to the bearing, the swinging arm has a track 21 in the form of an arc of circumference. When said arm travels through such angular displacement as to bring the bearing 14 beyond the position of full load, the track 21 slides on the rocket arm roller 19 which then forms a fixed fulcrum. <IMAGE>

Description

SPECIFICATION A pneumatic pressure governor in braking elements of vehicles as a function of load This invention relates to pneumatic pressure governors in the braking elements of vehicles as a function of load, and more particularly is concerned with pressure governors involving a variable fulcrum type of rocker arm for proportioning the braking pressure and a load responsive oscillating or swinging arm which by its free end provided with bearing or the like causes the fulcrum displacements.

As well known, in this type of governors, the strain or stress is transmitted by the variable fulcrum rocker arm from the drive or control piston to the reaction piston in an amount depending on the load acting on the vehicle, so as to avoid the wheel jamming when the load is zero or minimum.

In order to sense the load, the arm is through a suitable linkage connected to the stationary part or axle of the vehicle, while the governor is mounted on the suspended part or frame of the vehicle.

As the load on the vehicle varies, the arm takes different angular positions, thus varying the position of the bearing and accordingly the position of the fulcrum on the rocker arm. As a result, the length of the rocker arms will vary and accordingly the stress being transmitted by the drive or control piston to the reaction piston, the supply chamber of which is connected to the braking elements to be controlled.

Normally, the rocker arm has a curved surface, on which the bearing slides as carried by the arm end.

Under unloaded condition of the vehicle, the bearing takes an initial position on this surface and the governor controls a minimum delivery of pressure to the braking elements while, at full load, the bearing takes a final position on the sliding surface and the governor supplies a maximum pressure equal to that acting on the control or drive piston.

In the prior art governors, such as that shown in the French Patent No. 7,120,092, both the supply chamber of the control or drive piston and the chamber of the reaction piston are supplied through the pedal distributor, so that the maximum pressure in the controlled braking elements is the maximum pressure supplied by the distributor, independently of the travel of the arm on the rocker arm which may also exceed the position taken at full load.

Therefore, in such governors, the reply pressure can never exceed the control pressure.

On the other hand, where the chamber of the reaction piston is not supplied through the pedal distributor, but by a compressed air tank through a normally closed valve, as shown, for example in the governor according to the Italian Patent Application No. 23558 A/79 of June 14, 1979, still in the applicant's name, then the reply pressure, that is the pressure in the controlled braking elements, may take values higher than the control pressure when the oscillating or swinging arm and hence the end bearing moves on the rocker arm beyond the position of full load of the vehicle. This situation may occur when the vehicle is at full load and travels uneven road distances, having, for example, pits, steps, etc.

Thus, under such circumstances, the suspended part of the vehicle is subjected to oscillations due to the dynamic load causing angular movements or displacements of the arm beyond the position taken for the full load of the vehicle.

Underthe above specified conditions (full load and uneven road), should the drive act upon the brake pedal, the controlled braking elements would be supplied with a higher pressure than the control pressure, with resulting wheel jamming and higher stresses on the braking members.

It is the object of the present invention to provide a braking pressure governor for vehicles of the above mentioned type, in which the rocker arm fulcrum is maintained fixed at the position of full load of the vehicle for angular movements or displacements of the swinging or oscillating arm beyond said position of full load, so as to endure that the reply pressure in the controlled braking elements never exceeds the control pressure.

The above objects are accomplished by a pressure governor which, according to the invention, is characterized by a rocker arm having, at the position taken by the fulcrum under the conditions of full load of the vehicle, at least one rolling member and one oscillating or swinging arm having at the free end in addition to the bearing, at least one race or track in the form of an arc of circumference, having its center on the axis of rotation of the arm, which contacts the rolling member of the rocker arm when said arm travels through such angular movements or displacements as to bring the bearing beyond said position of full load, so that during the contact between said race or track and rolling member a fixed fulcrum is provided for the rocker arm.

According to a preferred embodiment, the rolling member comprises a roller arranged tranversely of the rocker arm and retained within a corresponding slot of the latter, while the arm race or track intended to cooperate with the rocker arm roller is provided by means of two end portions or sectors of the arm, having the bearing mounted therebetween.

Further details and characteristics of the invention will become evident from the following description and drawings referring by mere way of example to a preferred embodiment of the pressure governor.

In the accompanying drawings: Figure 1 is a schematic view showing the pressure governor provided with rocker arm and oscillating or swinging arm according to the invention; Figure 2 is a view showing a constructive solution for the pressure governor in a sectional view taken at the rocker arm and oscillating a swinging arm; Figure 3 is a plan view showing the rocker arm of Figure 2 carrying the roller; and Figure 4 is a sectional view of the governor of Figure 2 taken along line AA.

Referring to Figure 1, reference numerai 1 indicates the body of the pressure governor having two cylindrical cavities 2 and 3, in which a control drive piston 4 and a reply or reaction piston 5 slide respectively, these pistons 4 and 5 being kinematically interconnected by means of a variable fulcrum rocker arm 6.

The feed chamber 7 for the control or drive piston 4 is supplied through the pedal distributor 8 also providing for delivering compressed air to the braking elements 9 of the front or leading axle of the vehicle.

The feed chamber 10 for the reaction piston 5 is directly supplied from a tank 11 through a normally closed valve 12.

In turn, such a chamber 10 supplies the braking elements 13 of the rear axle of the vehicle, which are the braking elements controlled by the governor.

The variable fulcrum of the rocker arm 6 is provided by means of a bearing 14 arranged at the free end of an arm 15 oscillating about the axis of rotation 16 as the load acting on the vehicle varies.

To this end, said arm 15 is connected by a suitable linkage 17 to the axis of the braking section to be controlled. Therefore, this oscillating or swinging arm 15 displaces on a curved surface 6a of the rocker arm the bearing 14which, by acting as movable fulcrum, causes a variation in the length of the rocker arm and accordingly in the stress transmitted by the control or drive piston 4 to the reaction piston 5, and hence also varies the pressure value in chamber 10 with respect to that in the control chamber 7.

At unloaded vehicle, the oscillating or swinging arm 15 and bearing 14 take the position shown by full line on the drawing. Thus, under these conditions, the bearing is at the initial position of the above mentioned surface 6a.

At full load of the vehicle, said arm 15 and bearing 14 take a position, in the following referred to as full load position, acording to the axis X-X in this case, said bearing 14 is at the end of the sliding surface 6a.

The governor also comprises a pressure limiting device 18, not forming part of the invention, which is effective at the initial braking step.

For a more detailed description of both the governor and pressure limiting device 18, reference is made to the aforementioned Italian PatentApplication No. 23558 A/79 filed on June 14,1979.

At the end of the surface 6a, that is at the position taken by the fulcrum under the conditions of full load of the vehicle (see axis X-X), the rocker arm 6 has a transverse roller 19 which is retained in a corresponding slot 20 of the rocker arm, and at the free end said oscillating or swinging arm 15 has in addition to and rearwardly of the bearing 14 a race or track 21 in the form of an arc of circumference, having its center on the axis 16 and intended to contact said roller 19 as soon as said arm 15 travels through such angular movements or displacements as to bring said bearing 14 beyond said position of full load. In the figure, a general position is shown by dashed line beyond the full load position X-X, as achieved by the arm and bearing during the oscillation.

Of course, positions beyond the full load line X-X are achieved by the oscillating part 14-15 when the vehicle is atfull load and travels through uneven road lengths, so as to be momentarily subjected to higher dynamic loads than the full load. As the race or track 21 comes into contact with the roller 19, the rocker arm fulcrum is maintained at fixed position along the axis X-X, with the result that the length of the rocker arms is unchanged and accordingly the reply or reaction pressure in chamber 10 and braking elements 13 can never exceed the pressure value set for the full load position which is normally coincident with the value of the control pressure in chamber 7. From that moment, the bearing 14 freely continues its travel without contacting the rocker and since the latter has a depressed portion 6b from' the slot 20.The race or track 21 is sufficiently long to ensure the contact with the roller 19 even for displacements of arm 15 of considerable amplitude.

A preferred embodiment of both the rocker arm 6 carrying the roller 19 and arm 15 carrying, in addition to the bearing, said race or track 21 is shown in Figures 2,3 and 4, in which the corresponding parts have been indicated by the same numerals or symbols. At the intermediate zone, the rocker arm 6 has the transverse slot 20 of circular shape for accomodating said roller 19.

This slot is at the end of the surface 6a cooperating with the bearing 14 and at the beginning of the depressed part 6b.

At the top said slot is half-closed, so that the roller 19 is mounted therein by sidewise insertion and is blocked in place by means of two side pins 22.

The slot extends in two side expansions 23 intended for abutment against two ledges 24 of the governor lid 25 to stop the rocker arm displacement in case of breakage in the lever 15 or linkage 17.

The sliding race or track on the roller 19 is provided by two circular sectors 21 forkwise arranged at the free end of arm 15, between which the bearing 14 is mounted at advanced position.

Thus, during the arm movements or excursions beyond the full load position, the sectors will slide on the side parts or portions of the roller, while engaging with the central part or portion of the latter said bearing 14, but limitedly to the passing or overtaking moment.

Therefore, the roller could comprise three elements or pieces, and namely a central piece and two side pieces.

Claims (5)

1. A pneumatic pressure governor in the braking elements of vehicles as a function of load, and more particularly a governor of the type involving a variable fulcrum rocker arm for proportioning the braking pressure and a load responsive oscillating or swinging arm which, by its free end provided with bearing orthe like, causes the fulcrum displace ments on the rocker arm, characterized in that said rocker arm has at the position taken by the fulcrum under the conditions of full load of the vehicle at least one rolling member, and that at the free end said oscillating or swinging arm has in addition to the bearing at least one race track in the form of an arc of circumference, having its center on the axis of rotation of the arm, contacting said rolling member when said arm travels through such angular move ments or displacements as to bring said bearing beyond said position of full load, so that during said contact between said race or track and rolling member a fixed fulcrum is provided for the rocker arm.

2. A pressure governor according to Claim 1, characterized in that said rolling member comprises a transverse roller retained within a corresponding slot of the rocker arm, while the arm race or track, intended to cooperate with the rocker arm roller, is provided by means of two end sectors or portions of said arm, said bearing being mounted therebetween.

3. A pressure governor according to Claim 2, characterized in that the roller housing slot is half-closed, so that the roller is assembled therein by sidewise insertion and the axial constraint of the roller is assured by removable means.

4. A pressure governor according to Claims 2 and 3, characterized in that the roller housing slot extends in two side expansions of the rocker arm intended for abutment with the apparatus lid to stop the rocker arm displacement in case of failure in the control linkage or arm.

5. A pressure governor, substantially as hereinbefore described with reference to the accompanying drawings.