Combined braking system and vehicle comprising the combined braking system

Abstract

The braking system comprises a hydraulically actuated first braking device for a first wheel of the vehicle, and a mechanically actuated second braking device for a second wheel of the vehicle and functionally associated with an actuating member by means of a cable The cable is slidable inside a flexible pushing sheath. The braking system further comprises a combined braking valve, having a piston and a cylinder containing a brake fluid. The piston subdivides the cylinder into two chambers. The first chamber is fluidly connected to the inlet of the cylinder and the second chamber is fluidly connected to the outlet of the cylinder. The cable slides through the piston and the flexible pushing sheath is arranged in such a way that the first end of the flexible pushing sheath is constrained to the piston so as to generate an axial thrust as a result of the cable being pulled by the second actuating member.

Description

COMBINED BRAKING SYSTEM AND VEHICLE COMPRISING THE COMBINED BRAKING SYSTEMDESCRIPTIONTECHNICAL FIELD

[0001] The present invention relates to braking systems for vehicles, for example, but not exclusively, straddle-type vehicles with two or three wheels. Specifically, the invention relates to improvements to combined braking systems.BACKGROUND TO THE INVENTION

[0002] As is known, in the field of motorcycles and other straddle-type vehicles, there is a need to perform combined braking, i.e., such that - by acting on a single actuating member, such as a lever or pedal - simultaneous braking is achieved on both the front brake and the rear brake. This need arises from safety reasons, since the dynamic stability of the vehicle can be severely compromised by unbalanced braking between the axles of the vehicle. Indeed, in the absence of combined braking, dangerous yaw phenomena and loss of traction of the vehicle may occur. Some national legislations have made it compulsory to use braking systems for motorcycles that impose combined braking.

[0003] Solutions for braking systems that enable combined braking, i.e., the simultaneous actuation of the front and rear brakes, through a single command applied by means of a lever or a pedal, are available on the market

[0004] Typically, these combined braking systems comprise a hydraulically actuated first braking device and a mechanically actuated second braking device, by means of a cable slidably housed in a sheath, for example to form a Bowden cable. A combined braking valve is configured such that by acting on the mechanically actuated braking device, the hydraulic braking is also activated. An example of a combined braking system is disclosed in CN206012862. In this known braking system, the thrust generated by the pushing sheath is transferred from a thrust end of the pushing sheath to a piston of the combined braking valve by means of a complex mechanical linkage system, comprising a lever hinged to a shaft integral with the cylinder of the combined braking valve. The lever oscillates under the thrust of the pushing sheath and transfersthe thrust to the piston of the combined braking valve by means of an oscillating thrust pin.

[0005] A different combined braking valve is disclosed in EP3599151. In this different type of valve, the pushing sheath and the cable are arranged coaxially with the piston of the combined braking valve. Unlike the valve disclosed in CN206012862, in this second known device the piston does not feature a head with a seal that subdivides the valve cylinder into two chambers; rather, it is configured such that in any position of the piston within the cylinder there is always a brake fluid leakage along the piston, between the inlet and the outlet.

[0006] The combined braking systems of the prior art often have a complex structure, or have operating faults due to the internal hydraulic structure of the combined braking valve.SUMMARY

[0007] According to one aspect, a combined braking system is disclosed herein that overcomes, wholly or in part, the drawbacks of known systems.

[0008] In embodiments disclosed herein, the braking system comprises a hydraulically actuated first braking device adapted to be operationally connected to a first wheel of the vehicle and functionally associated with a first actuating member, for example a lever on the handlebar of the vehicle, or a pedal. The braking system further comprises a mechanically actuated second braking device adapted to be operationally connected to a second wheel of the vehicle and functionally associated with a second actuating member by means of a cable. The cable is slidable inside a flexible pushing sheath. The braking system further comprises a combined braking valve, advantageously constrainable to a frame of the vehicle between the first braking device and the second braking device. The combined braking valve comprises a piston slidable in a longitudinal direction within a cylinder containing a brake fluid. The cylinder comprises an inlet fluidly connected to a hydraulic pump actuated by the first actuating member, and an outlet fluidly connected to the first braking device. The piston comprises a head with a sealing gasket, adapted to subdivide the cylinder into a first chamber and a second chamber sealingly separated from each other by the sealing gasket. The first chamber is fluidly connected to the inlet of the cylinder and the secondchamber is fluidly connected to the outlet of the cylinder. Characteristically, the cable slides through the piston of the combined braking valve, along the longitudinal direction of movement of the piston within the cylinder of the combined braking valve. Furthermore, the flexible pushing sheath is arranged in such a way that the first end of the flexible pushing sheath is constrained to the piston so as to generate an axial thrust on the piston as a result of the cable being pulled by the second actuating member.

[0009] Further advantageous characteristics and embodiments of the braking system are described below with reference to the accompanying drawings, and are defined in the dependent claims.

[0010] A further object of the invention is a vehicle, in particular a motor vehicle, for example a straddle-type motor vehicle, such as a scooter or a motorcycle with two, three or four wheels, comprising a braking system as defined above.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will be better understood by following the description and the accompanying drawings, which illustrate exemplary and non-limiting embodiments of the invention. More particularly, in the drawings:Fig. l is a schematic, axonometric view with parts removed of a straddle-type motor vehicle with a braking system according to the present invention;Figs. 2 and 3 are longitudinal sections of the combined braking valve in two different operating conditions, and more precisely Fig. 2 in a condition of second braking device deactivated and Fig. 3 in a condition of second braking device activated;Fig. 4 is a section analogous to the section of Figs. 2 and 3 with the cable and sheaths removed; andFig. 5 is a longitudinal section of a combined braking valve in a further embodiment.DETAILED DESCRIPTION

[0012] In Fig. 1, a vehicle 1 is schematically illustrated, on which a braking system according to the present invention may be installed. For greater clarity and simplicity of the drawing, parts of the vehicle have been removed. In the illustrated example, the vehicle l is a two-wheeled vehicle, comprising a frame 3, a rear driving wheel 5 and afront steering wheel 7. The front steering wheel 7 is supported by a fork 9 constrained to a steering column 12 which is rotatably housed in a steering tube 10. The steering column 12 is integral with a handlebar 11.

[0013] The engine and the saddle of the vehicle 1 are omitted for greater clarity and simplicity of representation.

[0014] The vehicle comprises a braking system 16, which in turn comprises a first braking device 17 and a second braking device 19. In the illustrated embodiment, the first braking device 17 is associated with the front steering wheel 7 and the second braking device 19 is associated with the rear driving wheel 5. The first braking device 17 is a hydraulic braking device, i.e., hydraulically actuated by means of a pump that pressurizes a brake liquid circuit, typically oil, hereinafter referred to as "brake fluid." The second braking device 19 is a mechanically actuated braking device, by means of a cable 20, for example a Bowden cable, as described further below. An inverted arrangement is not excluded, with the mechanically actuated braking device 19 associated with the front steering wheel 7 and the hydraulically actuated braking device 17 associated with the rear driving wheel 5.

[0015] In the illustrated embodiment, the first braking device 17 comprises a disc brake, with a disc 17.1 integral with the front steering wheel 7 and a hydraulically actuated brake caliper 17.2. The second braking device 19 comprises a drum brake, with a shoe not visible in detail in Fig. 1, actuated by the cable 20.

[0016] The first braking device 17 is actuated by the rider by means of a first actuating member. In the illustrated example, the first actuating member takes the form of a brake lever 13 carried by the handlebar 11. The brake lever 13 activates a hydraulic pump 14 that pressurizes the brake fluid toward the first braking device 17, through a hydraulic circuit described in greater detail below.

[0017] The second braking device 19 is actuated by the rider by means of a second actuating member. In the illustrated example, the second actuating member takes the form of a brake lever 15, also carried by the handlebar 11 and more precisely on the opposite side with respect to the brake lever 13, so that the rider can activate the first braking device 17 and / or the second braking device 19 separately or in combination.

[0018] In other embodiments, not shown, either of the two actuating members may take the form of a pedal, rather than a lever associated with the handlebar 11 of the vehicle 1.

[0019] The braking system 16 comprises a combined braking valve 21, described in detail below with reference to Figs. 2 to 4, which has the purpose of generating a combined braking effect on the front steering wheel 7 and the rear driving wheel 5 when the rider acts only on the second actuating member 15.

[0020] As will be described in greater detail below, the hydraulic circuit that actuates the first braking device 17 comprises: a first conduit 23, for example a flexible tube, extending from the pump 14 to the combined braking valve 21; and a second conduit 25, extending from the combined braking valve 21 to the braking device 17.

[0021] Conversely, the mechanical actuation of the second braking device 19 comprises, as already indicated, a flexible and substantially inextensible cable 20, for example made of steel, which extends from the second actuating member 15 to the second braking device 19, and which is housed in a first flexible sheath 27, hereinafter referred to as flexible pushing sheath, or simply pushing sheath, and in an additional flexible sheath 29. The cable 20 extends through the combined braking valve 21, as described in greater detail below.

[0022] Figs. 2, 3, and 4 each show a longitudinal section of the combined braking valve 21, respectively: in a condition of second braking device deactivated; in a condition of second braking device activated; with the cable removed.

[0023] In the illustrated embodiment, the combined braking valve 21 comprises a body 31 that can be fixed to the frame 3 of the vehicle 1, for example. For this purpose, fixing members may be provided on the body 31, for example eyelets 33. Inside the body 31 of the combined braking valve, a cylinder 35 is formed, within which a piston 37 is slidably housed. As described below, the piston 37 is axially movable inside the cylinder 35, in a longitudinal direction (arrow f37) parallel to the axis of the cylinder 35.

[0024] The piston 37 comprises a head 37.1 provided with a sealing gasket 39, for example a lip sealing gasket. The head 37.1 with the lip sealing gasket 39 subdividesthe cylinder 35 into two chambers, respectively: a first chamber 35.1 and a second chamber 35.2. The two chambers 35.1 and 35.2 have a variable volume depending on the position of the piston 37. In the condition of Fig. 2, the first chamber 35.1 has a volume practically equal to zero, since the piston 37 is entirely translated toward the right inside the cylinder 35.

[0025] The first chamber 35.1 is fluidly connected to an inlet 41 of the combined braking valve 21. The inlet 41 is in turn fluidly connected to the first conduit 23. The inlet 41 is fluidly connected to the cylinder 35 through two inlet ports 41.1 and 41.2 that are axially offset from each other, i.e., in the longitudinal direction of the axis A-A of the cylinder 35, for the reasons explained below.

[0026] The body 31 of the combined braking valve 21 further comprises an outlet 43, fluidly connected to the second chamber 35.2 of the cylinder 35 and connected to the second conduit 25.

[0027] The piston 37 comprises a shank 37.2 extending axially outside the body 31 of the combined braking valve 21, and a stem 37.3 extending axially in the opposite direction with respect to the shank 37.2. The head 37.1 of the piston 37 is thus located in the middle between the shank 37.2 and the stem 37.3.

[0028] In the illustrated embodiment, a seat 45, into which a first end 27.1 of the pushing sheath 27 is inserted, is integral with the shank 37.2. A second end 27.2 (Fig. 1) of the pushing sheath 27 bears against a fixed point, for example integral with the handlebar 11.

[0029] In some embodiments, a flexible seal 47, for example of the bellows type, is arranged between the seat 45 and the body 31 of the combined braking valve 21, to prevent or reduce the entry of dust or other debris inside the combined braking valve 21. An additional sealing ring 49 may be provided at the end of the body 31 of the combined braking valve 21, through which ring the shank 37.2 of the piston 37 extends.

[0030] In some embodiments, the stem 37.3 of the piston 37 is axially guided in a guide hole formed in a closing member 51 of the cylinder 35. The closing member 51 is applied to the end of the cylinder 35 opposite to the shank 37.2 of the piston 37 andtherefore opposite to the first end 27.1 of the pushing sheath 27. The closing member 51 may be provided with a sealing gasket 53 and with a stop ring 55, forming a bearing for an elastic member 57, which stresses the piston 37 toward a deactivated position, illustrated in Fig. 2, in which the piston 37 is pushed entirely toward one end of the cylinder 35, nullifying the internal volume of the second chamber 35.2 defined by the piston 37 in the cylinder 35.

[0031] The closing member 51 is provided with a through-opening, i.e., an axial through-hole, through which the cable 20 extends.

[0032] In the illustrated embodiment, the elastic member comprises a helical spring coaxial with the piston 37 and in particular arranged around the stem 37.3 of the piston.

[0033] The piston 37 is axially bored and forms a continuous passageway for the cable 20, which can thus slide through the piston 37 of the combined braking valve 21 in the longitudinal direction, i.e., in the direction (arrow f37) along which the piston 37 slides in the cylinder 35.

[0034] In some embodiments, a seat 58 for a first end 29.1 of the additional flexible sheath 29 is associated with the closing member 51. The second end 29.2 of the additional flexible sheath 29 is connected to, and bears against, a stationary point near the second braking device 19 (Fig. 1).

[0035] The operation of the braking system described above is as follows.

[0036] When the vehicle 1 is moving and not braking, the combined braking valve 21 is in the condition illustrated in Fig. 2. The pressure of the brake fluid, typically oil, that fills the conduit 23, the cylinder 35, and the conduit 25 is at a limited pressure, such as not to cause the activation of the first braking device 17. The cable 20 is in a rest condition, not stretched.

[0037] If the rider activates the first braking device 17 by means of the first actuating member 13, the brake fluid is pushed by the pump 14 into the conduit 23, into the inlet 41 of the combined braking valve 21, and, through the inlet port 41.1, into the second chamber 35.2 of the cylinder 35. From here, through the outlet 43, the brake fluid flows into the conduit 25 and actuates the first braking device 17, for example by closing the caliper 17.2 against the disc 17.1. The piston 37 remains in the position of Fig. 2, andthe vehicle 1 is braked by applying a braking torque on the front steering wheel 7 only.

[0038] If the rider activates the second braking device 19 by means of the second actuating member 15, this action causes the cable 20 to be pulled. The first effect caused by the pulling of the cable 20 is the activation of the second braking device 19, for example the closing of the shoes against the drum of the drum brake 19. The cable 20 pulled by means of the actuating member 15 slides inside the pushing sheath 27, the axial bore of the piston 37, the closing member 51 and the additional flexible sheath 29. The latter can be adjusted by means of an adjusting device 61 mounted on the closing member 51, to adjust the position of the ends of the additional flexible sheath 29 and to optimize the operation of the second braking device 19.

[0039] Due to the curvature of the Bowden cable formed by the cable 20 and the pushing sheath 27, the latter exerts a thrust, equal and opposite to the traction on the cable 20, which is discharged onto the constraint formed by the bearing of the first end 27.1 of the pushing sheath 27 on the seat 45, when no axial movement is permitted at the other end of the pushing sheath 27. This thrust results in an axial force applied directly and coaxially to the piston 37. When the thrust generated by the pushing sheath 27 as a result of the pulling of the cable 20 exceeds the elastic force generated by the elastic member 57, the piston 37 begins to slide in the cylinder 35 toward the closing member 51.

[0040] The translation of the piston 37 is in a direction such as to cause contraction of the elastic member 57 and an increase in the volume of the first chamber 35.1 as well as a reduction in the volume of the second chamber 35.2, as can be understood by comparing Figs. 2 and 3; Fig. 3 shows the position taken by the piston 37 when pushed by the pushing sheath 27 and the consequent increase in the volume of the first chamber 35.1 and reduction in the volume of the second chamber 35.2. The movement of the piston 37 of the combined braking valve 21 causes the injection of brake fluid from the second chamber 35.2 into the conduit 25 and the consequent activation of the first braking device 17.

[0041] Therefore, by activating the second braking device 19 by acting on the second actuating member 15, the rider also causes, with a certain delay, the activation of the first braking device 17, automatically and without the need to act on the first actuatingmember 13.

[0042] The translation of the piston 37 from the position of Fig. 2 to the position of Fig. 3 causes the closure of the port 41.1. The fluid communication between the first chamber 35.1 and the conduit 23 is ensured by the second port 41.2. In practice, when combined braking is activated, the piston 37 translates (arrow f37) from a first operating rest position (Fig. 2) to a second combined braking operating position (Fig. 3). In the rest position, the inlet 41 of the combined braking valve is arranged between the outlet 43 of the combined braking valve and the head 37.1 of the piston 37, so as to allow fluid connection between the inlet 41 and the outlet 43. In the combined braking operating position, the head 37.1 of the piston 37 is arranged between the inlet 41 of the combined braking valve 21 and the outlet 43 of the combined braking valve 21, or astride the inlet 41 of the combined braking valve 21, so that the fluid connection between the inlet and the outlet is interrupted by the piston head, and any movement of the piston 37 affects the pressure of the brake fluid exiting the combined braking valve, resulting in an action on the first braking device 17.

[0043] If the rider acts simultaneously on the first actuating member 13 and on the second actuating member 15, the braking action of the first braking device is more powerful.

[0044] The arrangement described enables smooth and efficient operation of the combined action braking system, with a simpler mechanical arrangement compared to combined braking systems of the prior art. The action of the pushing sheath 27 in the axial direction directly on the piston 37 and with the resultant of the thrust substantially coaxial with the piston 37 simplifies and makes the device more efficient. The combination of the axial passage of the cable 20 slidably guided through the piston 37, in combination with the hydraulic braking circuit comprising the two chambers 35.1 and 35.2 separated from each other by the head 37.1 of the piston with the sealing gasket 39, results in safe and smooth operation.

[0045] In the embodiment described above and illustrated in the accompanying figures, the pushing sheath 27 that acts on the piston 37 to cause the indirect activation of the first braking device 17 is represented by the flexible sheath arranged between the actuating member 15 and the combined braking valve 21. However, this is not the onlysolution. It is indeed possible to use the flexible sheath 29 as a pushing sheath. The only condition for the flexible sheath to act as a pushing sheath is that it forms a curve between the two ends and that both ends are each constrained to a respective constraint adapted to exert a reactive thrust force on the respective end of the sheath, one of which constraints is preferably fixed and the other is movable. The constraints may be, for example, simple bearings. When this condition is met, the pulling of the cable 20 causes a tendency of the flexible sheath to straighten, hence a tendency of its two ends to move apart. If these two ends are constrained, this generates a thrust on the constraint. If the pushing sheath is constituted by the flexible sheath 29, the braking system operates in the same manner as described above, but with the inlet 41 and outlet 43 of the brake fluid arranged in reverse.

[0046] In other words, the position of the combined braking valve 21 can be reversed, placing the pushing sheath 27 between the combined braking valve 21 and the second braking device 19, and placing the flexible sheath 29 between the combined braking valve 21 and the second actuating member 15.

[0047] Fig. 5 illustrates a longitudinal section of a combined braking valve 21 in a different embodiment. The same reference numerals indicate parts that are identical or equivalent to those described with reference to Figs. 2 to 4.

[0048] In the embodiment of Fig. 5, the combined braking valve 21 comprises a body 31 with fixing members, for example eyelets 33. Inside the body 31 of the combined braking valve 21, a cylinder 35 is formed, within which a piston 37 is slidably housed, axially movable inside the cylinder 35, in a longitudinal direction (arrow f37) parallel to the axis A-A of the cylinder 35.

[0049] The piston 37 comprises a head 37.1 provided with a sealing gasket 39. The head 37.1 with the sealing gasket 39 subdivides the cylinder 35 into two chambers, respectively: a first chamber 35.1 and a second chamber 35.2. The two chambers 35.1 and 35.2 have a variable volume depending on the position of the piston 37.

[0050] The first chamber 35.1 is fluidly connected to an inlet 41 of the combined braking valve 21. The inlet 41 is fluidly connected to the first conduit 23. The inlet 41 is fluidly connected to the cylinder 35 through two inlet ports 41.1 and 41.2 that are axially offset from each other, i.e., in the longitudinal direction of the axis A-A of thecylinder 35.

[0051] The body 31 of the combined braking valve 21 further comprises an outlet 43, fluidly connected to the second chamber 35.2 of the cylinder 35 and connected to the second conduit 25.

[0052] The piston 37 comprises a shank 37.2 which, unlike the shank 37.2 of Figs. 2 to 4, is formed by a component physically detachable from the remaining part of the piston 37. The shank 37.2 may be constrained to the remaining part of the piston 37, i.e., to the body of said piston 37, for example by means of a screw coupling.

[0053] Also in the embodiment of Fig. 5, the shank 38 extends axially outside the body 31 of the combined braking valve 21. The piston 37 further comprises a stem 37.3 extending axially in the opposite direction with respect to the shank 38. The head 37.1 of the piston 37 is thus located in the middle between the shank 38 and the stem 37.3.

[0054] In the embodiments illustrated in Fig. 5, similarly to the embodiment of Figs. 2 to 4, a bushing is provided that forms a seat 45 into which a first end 27.1 of the pushing sheath 27 is inserted. In this embodiment, the seat 45 - and more precisely the bushing that forms it - is fixed to the shank 38, which, as indicated above, is formed by an element physically distinct from the main body of the piston 37, but constrained to it. In other words, the end 27.1 of the pushing sheath 27 may be considered as indirectly constrained to the piston 37, if the element 38 is viewed as an intermediate component between the piston 37 and the seat 45. As described with reference to the previous embodiment, a second end 27.2 (Fig. 1) of the pushing sheath 27 bears against a fixed point, for example integral with the handlebar 11.

[0055] In some embodiments, a flexible seal 47 is arranged between the seat 45 and the body 31 of the combined braking valve 21. An additional sealing ring 49 may be provided at the end of the body 31 of the combined braking valve 21, through which ring the shank 38 of the piston 37 extends.

[0056] In some embodiments, the stem 37.3 of the piston 37 is axially guided in a guide hole formed in a closing member 51 of the cylinder 35. The closing member 51 is applied to the end of the cylinder 35 opposite to the shank 38 of the piston 37 andtherefore opposite to the first end 27.1 of the pushing sheath 27.

[0057] In this embodiment, by way of example, the closing member 51 consists of two axially aligned components 51.1 and 51.2.

[0058] The closing member 51 may be provided with a sealing gasket 53 and with a stop ring 55, forming a bearing for an elastic member 57, which stresses the piston 37 toward a deactivated position, in which the piston 37 is pushed entirely to the right in Fig. 5, nullifying the internal volume of the second chamber 35.2.

[0059] In the illustrated embodiment, the elastic member comprises a helical spring coaxial with the piston 37 and in particular arranged around the stem 37.3 of the piston.

[0060] The piston 37 is axially bored and forms a continuous passageway for the cable 20, which can thus slide through the piston 37 of the combined braking valve 21 in the longitudinal direction (arrow f 7) along which the piston 37 slides in the cylinder 35.

[0061] In this embodiment, a seat 58 for a first end 29.1 of the additional flexible sheath 29 is associated with the portion 51.2 of the closing member 51. The second end 29.2 of the additional flexible sheath 29 is connected to, and bears against, a stationary point near the second braking device 19 (Fig. 1).

[0062] Unlike the embodiment of Figs. 2 to 4, in the embodiment of Fig. 5 the piston 37 is stressed by two elastic members in combination: the elastic member 57, which in this embodiment is formed by a compression helical spring housed in the cylinder 35, and an additional elastic member 60, arranged between the body 31 and the bushing that forms the seat 45, formed, for example, by a further compression helical spring.

[0063] The operation of the combined braking valve 21 of Fig. 5 is analogous to that described above with reference to Figs. 1 to 4.

Claims

Claims1. A braking system (16) for a vehicle (1), wherein the braking system comprises:- a hydraulically actuated first braking device (17) adapted to be operationally connected to a first wheel (7) of the vehicle (1) and functionally associated with a first actuating member (13);- a mechanically actuated second braking device (19) adapted to be operationally connected to a second wheel (5) of the vehicle (1) and functionally associated with a second actuating member (15) through a cable (20); wherein the cable (20) is slidable inside a flexible pushing sheath (27) having a first end (27.1) and a second end (27.2);- a combined braking valve (21) adapted to be constrained to a frame (3) of the vehicle (1) between the first braking device (17) and the second braking device (19), wherein the combined braking valve (21) comprises a piston (37) slidable in a longitudinal direction within a cylinder (35) containing a brake fluid; wherein the cylinder (35) comprises an inlet (41) fluidly connected to a hydraulic pump (14) actuated by the first actuating member (13), and an outlet (43) fluidly connected to the first braking device (17); and wherein the piston (37) comprises a head (37.1) with a sealing gasket (39), adapted to subdivide the cylinder (35) into a first chamber (35.1) and a second chamber (35.2) sealingly separated from each other by the sealing gasket (39); and wherein the first chamber (35.1) is fluidly connected to the inlet (41) of the cylinder (35) and the second chamber (35.2) is fluidly connected to the outlet (43) of the cylinder (35);characterized in that the cable (20) slides through the piston (37) of the combined braking valve (21), along the longitudinal direction of movement of the piston (37) within the cylinder (35) of the combined braking valve (21); and in that the flexible pushing sheath (27) is arranged in such a way that the first end (27.1) of the flexible pushing sheath (27) is coupled to the piston (37) so as to generate an axial thrust on the piston (37) as a result of the cable (20) being pulled by the second actuating member (15).

2. The braking system (16) of claim 1, wherein the cable (20) and the flexible pushing sheath (27), combined together, form a Bowden cable.

3. The braking system (16) of claim 1 or 2, wherein the second end (27.2) of the flexible pushing sheath (27) is connected to the second actuating member (15) or to the second braking device (19).

4. The braking system (16) of any one of the preceding claims, wherein the flexible pushing sheath (27) is arranged in such a way as to form at least one curve between the second actuating member (15) and the combined braking valve (21); or between the combined braking valve (21) and the second braking device (19).

5. The braking system (16) of any one of the preceding claims, wherein the inlet (41) of the combined braking valve (21) is arranged between the outlet (43) of the combined braking valve (21) and a point where the first end (27.1) of the flexible pushing sheath (27) is connected to the piston (37) of the combined braking valve (21).

6. The braking system (16) of any one of the preceding claims, wherein the first end (27.1) of the flexible pushing sheath (27) is housed in a seat (45) integral and coaxial with the piston (37) of the combined braking valve (21), the seat (45) having a hole for the passage of the cable (20).

7. The braking system (16) of any one of the preceding claims, wherein the piston (37) comprises a head (37.1) configured to move between at least two operating positions:an operating rest position, where the inlet (41) of the combined braking valve (21) is arranged between the outlet (43) of the combined braking valve (21) and the head (37.1) of the piston, so as to allow the fluid connection between the inlet (41) and the outlet (43) of the combined braking valve (21); anda combined braking operating position, where the head (37.1) of the piston is arranged between the inlet (41) of the combined braking valve (21) and the outlet (43) of the combined braking valve (21), or astride the inlet (41) of the combined braking valve (21), so that the fluid connection between the inlet (41) and the outlet (43) of the combined braking valve (21) is interrupted by the piston head (37.1) and any movement of the piston affects the pressure of the brake fluid exiting the combined braking valve (21).

8. The braking system (16) of any one of the preceding claims,comprising an elastic member (57) adapted to stress the piston (37) of the combined braking valve (21) in a direction opposite to the thrust generated by the flexible pushing sheath (27) when the second braking device (19) is actuated; and wherein preferably the elastic member (57) is coaxial with the piston (37) and the cable (20).

9. The braking system (16) of any one of the preceding claims, comprising a closing member (51) for closing the cylinder (35), coaxial with the piston (37) and inserted into an end of the cylinder (35) opposite the first end (27.1) of the flexible pushing sheath (27); and wherein the closing member (51) comprises a through-hole for the passage of the cable (20).

10. The braking system (16) of claim 9, wherein the piston (37) comprises a guide stem (37.3) slidably engaged in the through-hole of the closing member (51); and wherein the guide stem (37.3) comprises a hole coaxial with the guide stem (37.3), through which the cable (20) extends.

11. The braking system (16) of claim 9 or 10, when dependent on at least claim 8, wherein the elastic member (57) is arranged between the closing member (51) and the head (37.1) of the piston.

12. The braking system (16) of any one of the preceding claims, comprising an additional flexible sheath (29), within which the cable (20) extends; and wherein the additional flexible sheath (29) extends:from the combined braking valve (21) to the second braking device (19), if the flexible pushing sheath (27) is arranged between the second actuating member (15) and the combined braking valve (21); orfrom the combined braking valve (21) to the second actuating member (15), if the flexible pushing sheath (27) is arranged between the second braking device (19) and the combined braking valve (21);13. The braking system (16) of claim 12, comprising an adjusting device (61) for the additional flexible sheath (29), adapted to adjust the position of the additional flexible sheath (29) relative to the combined braking valve (21).

14. The braking system (16) of claim 13, when dependent on at least claim 9, 10 or 11, wherein the adjusting device (61) is mounted on the closing member(51) of the cylinder (35) of the combined braking valve (21).

15. The braking system (16) of any one of the preceding claims, wherein the first braking device (17) comprises a disc brake, and the second braking device (19) comprises a drum brake.

16. The braking system (16) of any one of the preceding claims, wherein the inlet (41) of the cylinder (35) of the combined braking valve (21) comprises two inlet ports (41.1, 41.2) axially offset along the longitudinal extension of the cylinder (35), in such a way that the first chamber (35.1), into which the piston (37) subdivides the cylinder (35), is fluidly connected to the inlet (41) at any axial position of the piston (37) within the cylinder (35).

17. A vehicle (1) comprising: a front steering wheel (7); a rear driving wheel (5) and a braking system (16) according to any one of the preceding claims.

18. The vehicle of claim 17, wherein the first braking device (17) is operatively connected to the front steering wheel (7) and the second braking device (19) is operatively connected to the rear driving wheel (5).

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