Abstract:
A device for adjusting the free stroke for hydraulic brakes of bicycles or motorcycles of the type including a pump assembly ( 4 ) for operating an actuator element ( 16 ), and a communication line ( 17 ) for a working fluid, set between a pump assembly and an actuator element, the device including an expansion chamber ( 25 ) set along the communication line between the pump assembly and the actuator element.

Description:
FIELD OF THE INVENTION 
     The invention relates to a device for adjusting the free stroke of the lever in a hydraulic brake, particularly a brake for bicycles or motorcycles. 
     STATE OF THE ART 
     As is known, hydraulic brakes for bicycles are based upon the displacement of a piston governed by a lever operated by the user. The displacement of the piston pressurizes the hydraulic circuit and actuates the braking element, for example a caliper acting on a disk in the case of disk brakes. 
     The stroke performed by the pump piston from the resting position to the position of complete actuation is divided into two steps, the first step being referred to as “free stroke”, during which the fluid of the circuit is not brought to the operating actuation pressure, and the second step being the step of actuation proper. 
     The passage from one step to another is defined by the relative position of the piston with respect to a hole that sets the cylinder of the brake in communication with the fluid tank. 
     As long as the communication between the tank and the cylinder is open, during the stroke of the piston, the fluid can pass from the cylinder to the tank, and the pressure in the cylinder does not reach the operating pressure. 
     As soon as the stroke of the piston manages to close the communication between the tank and the chamber of the cylinder, the piston starts to compress the fluid, and the braking step starts. 
     It is moreover known that the amplitude of the free stroke, in addition to merely functional purposes, has the purpose of applying upon the action of the user a delay that serves to modulate braking as well as possible, and it is advantageous for said delay to be adjustable to adapt to the characteristics or preferences of the user and/or use of the brake. 
     Furthermore, said adjustment enables balancing of the actions of the front and rear brakes, the difference between which depends upon the different length of the tubes for delivery of the fluid, which extend from the cylinder of the brake pump to the cylinder of the piston caliper acting on the disk. 
     For this purpose, devices for adjusting the free stroke have been known for some time that are based upon the variation of the relative position of the piston with respect to the communication opening in such a way as to modify the amplitude of the first step of the stroke of the piston from the resting position to the actuation position. An example of said adjustment is described in the prior patent No. IT218037. 
     Adjusting devices of a known type present, however, the main drawback of being tied down to the constructional solution of the pump body of the brake, i.e., of the piston/cylinder assembly and of the tank associated thereto, and of being usable only in combination with that particular constructional solution. 
     A further drawback of known solutions is represented by their relative complexity and difficulty of use. 
     AIM OF THE INVENTION 
     With the present invention the aim is to overcome the drawbacks of the known solutions and to propose a device for adjusting the free stroke that can be applied to hydraulic brakes of different constructional geometry, that is convenient to use, and that ensures reliable operation. 
     SUMMARY OF THE INVENTION 
     The above purposes have been achieved by providing a device for adjusting the free stroke according to the annexed claims. 
     A first advantage of the invention consists in the possibility of applying the device to brakes of different construction, including pre-existing brakes. 
     A second advantage consists in the reliability and simplicity of construction of the device. 
     A third advantage lies in the ease of use and in the possibility of locating the device in a position readily accessible by the user. 
    
    
     
       LIST OF DRAWINGS 
       The above and further advantages will be better understood by any person skilled in the branch from the ensuing description and the annexed drawings, which are represented by way of non-limiting example and in which: 
         FIG. 1  shows a cross section of the device applied to a hydraulic brake for bicycles; 
         FIG. 2  is an enlarged cross-sectional view of the device; 
         FIG. 3  shows the cross section G-G of the device of  FIG. 2 ; and 
         FIG. 4  is an exploded view of the device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, a device according to the invention is illustrated for adjusting the free stroke of a hydraulic brake  1 . 
     In the example described, the brake  1  comprises an actuation lever  2 , which turns about a pin  3 , fixed with respect to the pump body  4  of the brake, said pump body  4  comprising a cylinder  5 , which communicates with a fluid tank  6  and with an outlet  7  for the fluid pressurized by the stroke of a piston  8 , which is mobile along the cylinder by action of the lever  2  via a thrust pin  9 , against the action of a counteracting return spring  12 . 
     In the case represented in the attached drawings, the tank  6  is preferably set at the distal end of the cylinder with respect to the stroke of the piston and has an opening  23 , which is closed by a removable plug  24 , the portion of the opening  23  in use facing and being applied to a portion of the handlebar  22 , for example by means of a gripping collar  25  of a type in itself known. 
     The thrust pin  9  is connected to the lever  2  by means of a threaded fit  21  engaging with a transverse hole of a cylinder  19  mounted on the lever  2 . 
     Preferably, the pin  9  can be rotated via an adjustment wheel  20  for varying the position of the lever  2 , which oscillates on the pin  3  thanks to the threaded fit, according to the preferences of the user. 
     Once again with reference to the example illustrated in the attached drawings, the piston  8  is constituted by a hollow stem  11  and is provided, at a proximal end, with a spherical seat  10  for housing a corresponding end of the pin  9  and, at the opposite distal end, with communication holes  13  between the internal cavity of the stem  11  and the outside thereof. 
     Set around the proximal part of the stem  11  is a first gasket  14 , which slides in a fluid-tight way along the internal wall of the cylinder  5  during the active stroke of actuation of the piston, whilst a second gasket  15  is set at the distal end of the cylinder in a fluid-tight way with respect to the outer surface of the stem  11 . 
     In the initial resting position ( FIG. 1 ), the active gasket  14  is set at the proximal end of the cylinder  5 , and the holes  13  are in communication both with the tank  6  and with the cylinder  4 . 
     When the lever  2  is operated, the piston starts its stroke, i.e., the step of free stroke, which continues until the stem  11  enters the tank  6  and the holes  13  are covered by the second gasket  15 , thus interrupting fluid communication between the tank  6  and the cylinder  5 . 
     From this point on, the active stroke of the piston  8  starts, with the cylinder  5  that is pressurized and the fluid that is pushed towards the outlet  7  towards the actuation element  16 , for example a caliper for disk brakes connected to the pump assembly  4  via a tube  17 . 
     According to the invention, connected at the outlet  7  of the pump assembly  4  is a device  18  for adjusting the free stroke of the pump piston  8 , i.e., the extent of the stroke performed by the lever  2  starting from the initial resting position, before the working fluid is sent to the actuator  16 . 
     The device  18  comprises a variable-volume chamber, which is set along the tube  17  in fluid communication between the pump assembly  4  and the actuator  16 , preferably at the start of the tube  17 , and is directly applied to the outlet  7  of the cylinder  5 . 
     The chamber is defined by the outer surface of a valve body constituted by a hollow sleeve  26 , fixed, for example with screw connection  28 , to a corresponding threaded opening  27  of the outlet  7 . 
     In greater detail, the sleeve  26  comprises a first portion  29  that can be inserted in a fluid-tight way into the opening  27  by means of a gasket  30  and that is separated by a ring  34  from a second portion  32 , which is external to the opening  27  and defines an outer cylindrical surface  33 . The first portion  29  of the sleeve  26  has an internal cavity  31 , which communicates in use with the outlet  7  of the cylinder  5  and proceeds along the sleeve  26 , widening into a second cavity  35 , which extends throughout the length of the second portion  32 . 
     In a position intermediate between the cavities  31 ,  35 , the sleeve  26  has transverse through holes  36 , which set the internal cavity  31 ,  35  in communication with the outer surface  33  of the second portion  32  at the ring  34 . 
     The second portion  32  moreover has, at its outer end,  36  a thread  37  and a slot  38  for housing an O-ring  39 . 
     The device moreover comprises an adjuster  40 , which is internally threaded for engaging with the thread  37  of the sleeve  26  and for being screwed on/unscrewed off this against the action of a thrust spring  41  and slides in a fluid-tight way on the ring  34  by means of a gasket  45 . 
     The spring  41  is housed on the outer surface  33  of the sleeve  26  between an abutment  42  of the adjuster  40  and a mobile gasket or ring  43 , which slides in a fluid-tight way between the inner cylindrical surface  44  of the adjuster  40  and the surface  33  and is set between the spring  41  and the ring  34 . 
     The outer surface  33  of the sleeve  26 , the inner surface  44  and the contrast  42  of the adjuster  40 , and the ring  34  define a variable-volume chamber  25 , which is regulated by screwing/unscrewing the adjuster  40  along the valve body  26 . 
     Illustrated in  FIG. 4  is an exploded view of assembly of the components just described. 
     In a preferred embodiment, the cavity  35  is suited to housing a nozzle  46  of a fast-coupling type in itself known, for setting the tube  17  in fluid communication with the first cavity  31 , said nozzle  46  terminating preferably in the proximity of the holes  36 . 
     In operation, the device is initially in the configuration of  FIG. 1 , with the lever  2  in the non-operated position. In this configuration, the entire circuit is pervaded with fluid not under pressure, the tank  6  communicates with the cylinder  5  via the holes  13 , and the mobile gasket  43  bears upon the ring  34 . 
     When the lever  2  is turned to carry out braking, the piston advances, the holes  13  are covered by the gasket  15 , and the cylinder  5  is pressurized. 
     From this point on, the pressurized fluid starts to flow through the port  5 , and in succession through the cavity  31  and the holes  36 , starting to push on the gasket  43 . As a result of the thrust of the fluid on the gasket  43 , the spring  41  starts to undergo compression up to complete filling of the chamber  25 . 
     During filling of the chamber  25 , the piston  8  continues its stroke, but the pressure of the fluid is not sufficient to operate the actuator  16 . 
     Hence, there is a free stroke of the piston, which terminates once filling of the chamber  25  has terminated, when the fluid is pushed through the tube  17  and the actuator  16  is operated. 
     Upon release of the lever  2 , the fluid under pressure re-enters the cylinder  5 , and the spring  41  performs the reverse stroke, bringing the gasket  43  back to bear upon the ring  34 . 
     According to the invention, by turning the adjuster  40  it is possible to increase or reduce the volume of the chamber  25  and hence the delay with which the fluid fills the chamber  25  before reaching the working pressure for operating the actuator. 
     Advantageously, thanks to the invention, adjustment of the free stroke of the piston in brakes or other hydraulic devices, however shaped, is extremely simple. 
     The device is suited to being integrated in the production of a hydraulic device or else to being inserted as accessory in a pre-existing hydraulic circuit. 
     Furthermore, the device thus conceived, in the embodiment illustrated, is easily accessible for the user and of extremely limited overall dimensions. 
     The example described refers to a hydraulic brake shaped as in the attached drawings, but it is understood that the device of the invention can be applied to hydraulic brakes otherwise devised. 
     The present invention has been described according to preferred embodiments, but equivalent variants may be conceived without departing from the sphere of protection of the invention. 
     In particular, the invention has been described with reference to the specific embodiment of the brake illustrated in the attached drawings, but it is understood that it may also be applied for adjusting the free stroke of hydraulic brakes of different conformation.