The present invention relates to a control apparatus, particularly for controlling the hydraulic brakes in the braking systems of vehicles. The control apparatuses of the hydraulic brakes of vehicles comprise cylinders that push the oil to the latter when the driver actuates the pedal of the brake located on board. These cylinders, so-called "master cylinders", are of the two-stage type, i.e. they have pistons with bodies that axially form two different continuous stages, each of which has a different diameter from the other.

Each stage runs in a chamber of suitable diameter; both the chambers are obtained in a liner that envelops the piston and is provided with ports both for connecting the pipes connected with the brakes of the vehicle and for connecting with an oil reserve sump.

When the driver presses the brake pedal, the piston moves into the slide chambers and in the first part of the piston stroke thereof it is the stage of greater diameter that is in action and which sends a considerable volume of oil to the brakes, so noticeable effort is required from the driver.

During this first part of the stroke, the noticeable volume of oil moved from the stage of greater diameter causes a rapid approach of the brake shoes to the respective friction surfaces, in a position ready for starting actual braking proper.

The latter starts when the action of the stage of greater diameter is progressively eliminated, by means of a valve provided for this purpose, and only the action of the stage of lesser diameter remains active, which enables the driver, with less effort required, to modulate the braking action with greater precision and convenience. Nevertheless, in certain cases, when the braking action ceases, noticeable hysterisis occurs inside the hydraulic

circuit that supplies the brakes; this occurs especially when the oil has great density.

This drawback creates certain problems.

A first drawback is that the brakes of the vehicle tend to remain driven for a few instants, even after the driver has terminated his action on the brake pedal.

A further problem is that the brake control pedal and the master cylinder do not return immediately to the same start position of the active stroke and the latter sucks oil from the reserve sump: therefore if a second braking action is required immediately after a first one that has just been performed, the driver is unable to measure out with precision the intensity of this second braking action because he is unable to rapidly perceive the point from which the subsequent active stroke of the brake pedal commences because it is noticeably shorter due to the volume of additional oil sucked by the reserve sump and introduced inside the control apparatus .

A further problem with known control apparatuses is that they have to be mounted in a horizontal position, otherwise the air-purging operations are not automatic and are substantially laborious to perform.

The object of the present invention is to improve the prior art. An object of the invention is to make a control apparatus that enables a rapid return of the fluid when the action of the driver on the brake pedal ceases.

Another object of the invention is to create a control apparatus that enables it to be prevented that at the end of a braking cycle the control means is in a different position from the one that it had initially.

Another object of the invention is to create a control apparatus that enables the operations of purging of the air from a user circuit, for example a braking circuit of vehicles, to be performed rapidly.

According to a first aspect of the invention, a control apparatus is provided, comprising cylinder means having a first end and an opposite second end and traversed axially by a slide chamber, piston means mounted slidingly in said slide chamber between a rest position and a distribution position to distributing ports, and vice versa, characterised in that said piston means is provided with first perimeter annular sealing means in said slide chamber, defining in the latter a first half-chamber facing said distributing ports and an opposite adjacent second half- chamber.

According to a second aspect of the invention it is provided for that in said first half-chamber there is a first pressure and in said second half-chamber there is a second pressure that is different from said first pressure.

According to a third aspect of the invention it is provided for that said first pressure is greater than said second pressure. According to a fourth aspect of the invention a method is provided particularly for facilitating the return of piston means mounted slidingly in chamber means of cylinder means provided with distributing ports (5) characterised in that it comprises: mounting annular means perimeterally on said piston means, arranged for forming a seal in said chamber means and pushing a fluid to said distributing ports; subdividing said chamber means with said annular means into two adjacent half-chambers, a first half-chamber facing said distributing ports and a second half-chamber facing an opposite part; sliding said piston means ¹ in said chamber means to said distributing ports creating a first pressure that is greater in said first half-chamber and a second pressure that is less in the adjacent half-chamber, such as to recall said piston means in a direction opposite said distributing ports. The braking apparatus and the method enable the recall of pistons that are slideable inside respective cylinders to be

facilitated using, in addition to the normal contrast thrust provided by spring means that is loaded by the piston sliding, also a sucking action determined by a vacuum that is created in one of the two half-chambers in which the slide chamber of the piston is divided, mounting on the piston a perimeter annular element that forms a seal with the walls of the slide chamber.

Further features and advantages of the invention will be clearer from the detailed disclosure of a control apparatus, illustrated by way of non-limitative example in the attached sheets of drawings, in which:

Figure 1 is a longitudinal section of a control apparatus in an initial configuration of delivery of pressurised oil to the brakes of a vehicle to start a braking cycle; Figure 2 is the corresponding schematic view of the longitudinal section of the control apparatus in Figure 1; Figure 3 is a longitudinal section of the apparatus" in Figure 1 in a braking phase. With reference to Figure 1, 1 indicates overall a control apparatus, particularly for controlling the delivery of pressurised fluid, for example oil, , to the brakes of a vehicle, in vehicle braking systems, that is not illustrated because it is known. The control 1 apparatus 1 comprises cylinder means 2 that has a first end 102 and an opposite second end 202 and is traversed axially by a slide chamber, indicated overall by 3.

In the slide chamber 3 piston means 4 is mounted that is slidable between a rest position, shown in figure 1 in which the piston means 4 is moved to the left part of an observer of the slide chamber 3, and a driving position illustrated in Figure 3, in which it is moved to the right, i.e. towards distributing ports 5 that connect the control apparatus 1 to the supply circuit of the brakes of a vehicle, and vice versa.

The piston means 4 is provided with first annular sealing means 6 forming a seal with the internal walls of the slide chamber 3 arranged on the perimeter; in practice, the annular sealing means 6 divides the slide chamber 3 into two half-chambers of which a first half-chamber 103 faces the distributing ports 5, and an opposite adjacent second half- chamber 203 is facing an opposite part, as better explained below. Between the cylinder means 2 and the piston means 4 guiding means 7 is interposed for guiding the sliding of the piston means 4 inside the slide chamber 3.

The annular sealing means 6 comprises a first annular washer 306 that rests on a second rigid ring 106 that envelops the piston means 4 and is made integral with the latter in the shifts with a rigid locking ring 206, for example a Seger circlip ring.

The guiding means 7 comprises an annular element 8 that is mounted on the first end 102 of the cylinder means 2 and is axialIy traversed by an opening 9 for the passage of the piston means 4.

Between the latter and the annular element 8 a first elastic sealing means 10 is interposed that comprises at least a washer 11 housed in a hollow seat 12 obtained in the internal face of the annular element 8. The piston means 4 comprises a first cylindrical segment 104 that has a first diameter O ₁ , and is received coaxially slidably in the opening 9 of the annular element 8; the first cylindrical segment 104 has a first end 104' that extends outside the cylinder means 2 and an opposite second end 104'' that faces inside the slide chamber 3 and that forms a first hollow axial seat 13.

The piston means 4 furthermore comprises a second cylindrical segment 204 that constitutes the coaxial extension of the first segment 104 to the distributing ports 5 and which has a second diameter Φ ₂ less than the first diameter O ₁ .

The second cylindrical segment 204 has a third end 204' that is received in the first hollow seat 13 and an opposite fourth end 204'' that shapes a second hollow seat 15. The first annular sealing means 6 has a diameter Φ ₃ that is greater than both that of the first diameter Φi and of the second Φ ₂ .

The first half-chamber 103 is in turn subdivided into a first portion 103' facing the second half-chamber 203, that has an internal diameter substantially coinciding with the diameter Φ ₃ of the first annular sealing means 6, and a second portion 103' ' facing the distributing ports 5 that has an internal diameter substantially coinciding with the diameter Φ ₂ . Between the second portion 103' ' and the second cylindrical segment 204 there is interposed second annular sealing means 14 that comprises a third washer 16 housed in a corresponding third hollow seat 17 that is obtained in the internal wall of the second portion 103' ' . The first portion 103' and the second portion 103' ' define a joining shoulder 18 in a common orthogonal transverse plane of mutual conjunction.

The second annular sealing means 14 is placed in a zone comprised between the distributing ports 5 and the joining shoulder 18, so as to be substantially adjacent to the latter.

The second cylindrical segment 204 has, near the fourth end 204'', radial communicating ports 19 for making the second hollow seat 15 and the first half-chamber 103 communicate together. The cylinder means 2 comprises, at the opposite second end 202, occluding means of the slide chamber 3 . The occluding means 20 axially forms conduit means 21 for connecting with fluid accumulating means 22. The occluding means 20 comprises a cap body 23 that has a threaded end 123 and engages a counter-threaded opening 24

obtained at the end of the second portion 103' ' that extends beyond the distributing ports 5.

The conduit means 21 is controlled by presettable first control valve means 25 that comprises a cylindrical element 26 that is mounted fixed in the second hollow seat 15 and has a fifth end 126 facing the annular element 8 and an opposite sixth end 226 facing the occluding means 20; inside the cylindrical element 26, there is mounted, slidable in an axial cavity 27 of the latter, a stem element 28 that has a seventh end 128 that faces inside the latter and an opposite eighth end 228 that extends outside the latter, through the sixth end 226, to the occluding means 20.

The first valve means 25 furthermore comprises a shutter body 29 that is mounted integrally, for example with mutual snap-connection means, on the eighth end 228 and which is received in a fourth hollow seat 30, with the interposition of elastic sealing means 129, which is obtained coaxially in the occluding means 20 and which communicates with the conduit means 21; between the occluding means 20 and the cylindrical element 26 first elastic contrast means 31 of presettable type is interposed; further second elastic means 32 of presettable type is interposed between the shutter body 29 and the fourth hollow seat 30, resting with the mutual ends on a transverse disc 229 and on a shoulder of the shutter body 29.

The cylindrical element 26 also has peripheral connecting openings 33 for connecting together the second hollow seat 15 and the axial cavity 27; the latter is connected to the hollow seat 15 also through openings 502 obtained in a transverse ring 501 that is housed between the fifth end 126 and a further shoulder that is obtained inside the second cylindrical segment 204.

The control apparatus 1 is also provided with purging means 34 for purging any air present inside the pressurised fluid pumped by the latter.

The purging means 34 comprises a further port 35 that is obtained in a transverse direction in the cylinder means 2 and which is arranged to connect the slide chamber 3 with the exterior. This further port 35 is provided with a mouth 37 for fitting a pipe and is controlled by valve control means 38. The valve control means 38 comprises a diaphragm body 138 placed on the bottom of the further port 35 to control the passage of the channel 238 that connects the further port 35 to the second portion 103' ' .

The diaphragm body 138 is placed at a preset distance from the concurrent end of the mouth 37, so as to be able to lift up from the support against the channel 238. A pipe 39, indicated by a dotted line in Figure 1, connects the further port 35 to the fluid accumulating means 22.

In the first hollow seat 13 there is received, as said previously, the third end 204' of the second cylindrical segment 204. The third end 204' forms a fifth internal and coaxial hollow seat 40 in which fifth valve control means 41 is haused.

The latter controls a connecting opening 42 that is connected to the slide chamber 3 through a port 43. In detail, the fifth valve control means 41 comprises a spherical shutter 44 that is normally kept supported against the opening 42 by a spring 45 interposed between the spherical shutter 44 and the bottom of the first hollow seat 13 and which is movable at opening by means of both the oil pressure in the first portion 103' , and by a pivot 46 that is maintained coaxially slidable in a central opening 42', obtained in the segment 204 and comprised between the spherical shutter 44 and the transverse ring 501. At the pivot 46 in the second cylindrical segment 204, corresponding transverse ports 47 are provided that lead into a common central conduit 48 that connects them with the second hollow seat 15.

The passage between the latter and the central conduit 48 is controlled by an elastic washer 49 that is traversed by the pivot 46 on which it forms a hermetic seal and which is normally kept in an occluding position in contact with the mouth of the central body 48 by means of a spring 50 interposed between the elastic washer 49 and the transverse ring 501.

The elastic washer 49 rests on a rigid transverse disc 49' that normally rests in turn on the edges of the central conduit 48.

Furthermore, the spring 50 is fitted on a spring-guide element 49' ' that is proper to it that rests on the elastic washer 49, on an opposite side with respect to the rigid transverse disc 49' and which has the further function of limiting the movement of the elastic washer 49 parallel to itself in the direction of the transverse disc 501. The operation of the control apparatus 1 is indicated below by referring by way of example, to the mounting and use thereof in a braking circuit for vehicles, and is as follows: when the driver of a vehicle has to brake, he presses the pedal 40 provided for that purpose in the vehicle.

The pedal 40 acts directly on the first cylindrical segment 104 of the piston means 4 making it advance in the direction of the cap body 23.

This advance causes the compression of the first elastic means 31 and the progressive retraction of the stem element 28 into the cylindrical element 26. The second elastic means 32, which before mounting in the fourth hollow seat 30 is compression preloaded, presses on the shutter body 29, which is no longer retained by the retracted stem element 28, and consequently occludes the conduit means 21 as can be seen in Figure 3. As the action of the driver on the pedal 40 continues, the annular means 6 pushes the fluid, in the case in point oil,

to the brakes, progressively increasing the pressure inside the half-chamber 103.

Owing to the movement of the second segment 204, the radial ports 19 go past the third washer 16 and, in this configuration, the slide chamber 3 is completely sealed.

The oil reaches the brakes of the vehicle going through the transverse ports 47, the openings 502, after lifting the elastic washer 49 and, through the peripheral openings 33, flowing first into the second portion 103' ' and from this into the supply ports 5.

The first part of the stroke of the piston means 4 moves a noticeable volume of oil pushed by the maximum diameter Φ ₃ section that moves the friction elements of the brakes near to the discs or to the drums, in a braking start position; the thrust action of the maximum diameter Φ ₃ progressively ceases with the start of the opening of the spherical shutter 44, opposed by the spring 45 set to a preset value and exceeded by pressure of the oil reaching inside the first portion 103' of the half-chamber 103. In this first part of the stroke, the effort that the driver has to apply to the pedal 40 is noticeable due to the pressure that it is necessary to reach to overcome the opposing action of the spring 45 until the spherical shutter 44 is opened; this pressure value acts on the first sealing means 6 mounted on the first segment 104 of the piston means 4, which has a diameter Φ ₃ that is greater than both the diameter O ₁ of the first segment 104 and the diameter Φ ₂ of the second segment 204. The progressive advance of the piston means 4 subdivides the slide chamber 3 into two half-chambers, 103 and 203, the first of which progressively decreases in volume whilst the second tends to increase in volume (see also Figure 3) . In particular, owing to the seal of the elastic ring 306, in the half-chamber 203 a strong vacuum is created whereas in the half-chamber 103 the pressure continues to increase

through the effect of the action of the driver on the pedal 40.

When the pressure inside the half-chamber 103 reaches a preset maximum value at which the valve control means 41 has been set, as mentioned previously, the shift of the spherical shutter 44 starts that opens the opening 42, by making the oil drip inside the half-chamber 203. In this way, the pressure inside the half-chamber 103 and therefore acting on the maximum diameter Φ ₃ , decreases progressively; simultaneously, the pressure inside the second portion 103' ' still increases due to the prolongation of the action of the driver on the brake pedal. A pressure difference is thus created between the second portion 103' ' and the first portion 103' of the first half- chamber 103, a pressure difference that acts on the transverse section of the pivot 46, keeping it in contact against the spherical shutter 44 that overcomes the force of the contrast spring 45 and keeps the oil drip open between the spherical shutter 44 and the opening 42 until the pressure inside the first portion 103' is eliminated: in this condition, the thrust action of the sealing means 6 having a diameter Φ ₃ is also eliminated.

The braking action then continues by means only of the action of the second cylindrical segment 204 that, having a diameter Φ ₂ less than the diameter Φ ₃ of the sealing means 6, offers less resistance to the advance and enables the driver to modulate braking more easily and sensitively. The sliding of the second cylindrical segment 204 makes the radial ports 19 go beyond the third washer 16: in this configuration, the second portion 103' ' is completely sealed and the thrust exerted by the driver on the pedal of the brake is transformed proportionally into braking action as the oil pushed by the second cylindrical segment 204 reaches the brakes through the distributing ports 5. When the action of the driver on the pedal 40 terminates, the distension of the spring 125 and the pressure inside the

second portion 103' ' make the piston means 4 slide in the opposite direction to the preceding one.

The return slide of the latter is facilitated by the vacuum that is created in both the first half-chamber 103 and in the second 203 and which is progressively compensated by the dripping of oil through the opening 42.

The return sliding of the piston means 4 recalls oil from the brakes with the action of the second cylindrical segment 204 that has a diameter Φ ₂ until the radial ports 19 go past the third washer 16 in the opposite direction to the previous one: when this occurs, the second portion 103'' is connected with the first half-chamber 103 equalising the pressure with the latter. During the backward stroke, the leaked oil inside the second half-chamber 203 flows inside the first half-chamber 103, lifting up the elastic washer 306 from the support on the rigid ring 106; the elastic washer 306, by lifting up, compresses the spring 406 and the vacuum inside the first half-chamber 103 and the second half-chamber 203 recalls the oil from the braking system.

The elastic means 31 rapidly returns the piston means 4 to the rest position and the stem element 28 slides completely out of the axial cavity 27, dragging with it the shutter body 29 that, consequently, opens the conduit means 21. In this way, the accumulating means 22 is made to communicate with the slide chamber 3 and provides possible volumes of oil missing and accidentally remaining inside the hydraulic braking circuit of the vehicle despite the recalling action of the piston means 4 during the return movement.

If the cylinder means 2 is mounted so that the longitudinal axis thereof is horizontal, or is substantially horizontal, the air is purged through the further port 35, which is connected to the accumulating means 22, inside which the purged air is collected.

In fact, possible air present in the first half-chamber 103 flows through the further port 35 pushed by the piston means 4 in the braking movement, before the first sealing means 6 goes past the channel 238, the opening of which is regulated by the disc 138: this disc 138 enables the air to be sent in a single direction without any possibility of return to the oil accumulating means 22.

If the cylinder means 2 is mounted so that the longitudinal axis thereof is vertical, or substantially so, it is not necessary to provide the presence of purge port 35 and the complete purge occurs through the conduit means 21 to which the air rises spontaneously through floating in the oil: also in this case, the air is collected inside the accumulating means 22. It is pointed out that if no purge port 35 is provided in the control apparatus 1 and accidentally a total lack of seal should occur in the third washer 16 and in the elastic washer 49, for example due to damage thereto, it is nevertheless possible to carry out emergency braking of the vehicle, albeit with the driver exerting great force on the pedal 40.

The necessary braking pressure is anyway provided by the thrust of the first cylindrical segment 104, which has a diameter Φi, and which advances : the hydraulic seal is ensured in this case by the washer 11 and the shutter body 29 which, with advancing, shuts the conduit means 21, forcing the oil to flow through the distributing ports 5.