FAST-FILL MASTER CYLINDER

Abstract: A fast-fill master cylinder with at least one piston received in a bore and defining therewith a primary chamber and an auxiliary chamber and further carrying valve means which control fluid communication between said auxiliary chamber and either said primary chamber or a fluid reservoir during a brake application. In order to facilitate the machining of the cylinder bore (28), this latter is given a substantially uniform diameter except for an annular groove (54) in which is held in fixed axial position the sealing member (56) which limits the auxiliary chamber. For use particularly in automotive braking systems.

Description: FAST-FILL MASTER CYLINDER The present invention relates to a fast-fill master cylinder, particularly for use in braking systems for automotive vehicles. A fast-fill or quick take-up master cylinder permits larger brake lining clearances with a rotatable member so that lining drag is substantially eliminated. Such a master cylinder, as disclosed for instance in USA Patent No. 4 170 386, usually comprises a housing with a stepped bore and a primary piston sealingly engaging the stepped bore at a small diameter section and a large diameter section to substantially define a quick take-up chamber. When the piston is moved during a braking application, fluid within the quick takeup chamber is pressurized in response to contraction of the quick take-up chamber and communicated via a suitable passage to a primary chamber. During the manufacture cf the quick take-up master cylinder it is critical to maintain the concentricity between the small diameter section and the large diameter section of the stepped bore. The primary piston sealingly engages both sections and is movably disposed within both sections so thE any eccentricity between the sections will cause the primary piston to wedge within the stepped diameter bore. The present invention has for its object to overcome this drawback of the known constructions by providing a fast-fill or quick take-up master cylinder having a bore of substantially uniform diameter while still performing its intended function as satisfactorily as they do. This object is achieved, according to the teaching of this invention, and starting from a fast-fill master cylinder of the kind comprising a housing defining a fluid reservoir and a bore for movably receiving at least one piston which cooperates therewith to define a primary chamber and an auxiliary chamber both communicating with said reservoir in a rest or brake release position of said one piston, said one piston being movable within said bore to develop fluid pressure within said primary and auxiliary chambers during a braking application and carrying valve means responsive to the fluid pressure built up within said chambeisto control fluid communication between the auxiliary chamber and either the primary chamber or the reservoir, said auxiliary chamber being defined between a recessed portion of said piston, the inner wall of the bore and a resilient sealing member held in a fixed axial position with respect to said bore and designed so as to permit fluid communication between the auxiliary chamber and the reservoir when the piston is in its rest position and to block said communication upon initial movement of the piston from this position, thanks to the fact that said resilient sealing member is held in a recessed portion of the housing bore formed between two bore sections of substantially same diameter, and divides the volume between the recessed portion of the piston and the housing bore into two variable volume chambers, namely the proper auxiliary chamber and a further chamber which is permanently communicated with the reservoir. In a preferred embodiment of the invention, the recessed portion of the housing bore consists of an annular groove of substantially rectangular cross section the bottom wall of which communicates with the reservoir, and the resilient sealing member is susbstantially X-shaped in cross-section and includes a first pair of opposite lips engaging the lateral faces of said annular groove and a second pair of opposite lips engaging the bottom wall of the recessed portion of the piston. Furthermore, the lips of the first pair are each provided with circumferentially spaced tabs which define apertures for fluid communication between the reservoir and said further and auxiliary chambers respectively. The sealing member thus cooperates with the piston anc housing to open communication between the reservoir and auxiliary chamber in the rest or brake release position. The reservoir and auxiliary chamber rena open during initial movement of the piston relative to the sealing member so as to bleed the auxiliary chamber to the reservoir. Further movement of the piston relative to the sealing member closes communication between the auxiliary chamber and the reservoir and communicates fluid from the auxiliary chamber to the primary chamber. When a predetermined pressure level is reach ed within the primary chamber, the auxiliary chamber is either vented or meter ed to the reservoir. Upon termination of braking, the piston retracts to its rest position and the sealing member provides for communication of fluid from the reservoir to the auxiliary chamber to replenish the latter. These and other features of the invention will become more readil apparent from reading the following description of some preferred embodiments given by way of examples only, and with reference to the accompanying drawing in which - Figure 1 is a schematic illustration of a braking system having a master cylinder shown in cross-section which is constructed in accordance with the present invention ; - Figure 2 is an enlarged view of the encircled portion of Figure 1 - Figure 3 is an enlarged view similar to Figure 2 showing a first alternative embodiment ; and - Figure 4 is an enlarged view similar to Figure 2 showing a second alternative embodiment. In the brake system of Figure 1, a brake pedal 10 is coupled to a master cylinder 12 via an input rod 14 and the master cylinder 12 communicates with brake assemblies 16 and 18 via conduits 20 and 22, respectively. When the pedal 10 is actuated by a vehicle operator the input rod is moved into the master cylinder to generate fluid pressure in a manner hereinafter described so that the generated fluid pressure is communicated via conduits 20 and 22 to their respective brake assemblies, thereby effecting a brake application. The master cylinder 12 includes a housing 24 defining a split reservoir at 26. The reservoir communicates with a bore 28 via ports or openings 30, 32, 34 and 36. The bore 28 movably receives a primary piston 38 coupled to the input rod 14 and a secondary piston 40. The primary piston 38 cooperates with the secondary pistcn 40 to substantially define a primary chamber 42 therebetween and the secondary piston cooperates with the end wall 44 of bore 28 to substantially define a secondary chamber 46. The primary chamber 42 communicates with conduit 20 and the secondary chamber 46 co-ni- cates with conduit 22. A first spring 48 biases the secondary piston 40 away from end wall 44 and a second spring 50 biases the primary piston 38 away from secondary piston' 40 against a snap ring 52 to define a rest position for the primary piston 38. In accordance with the invention the bore 28 is substantially uniform in diameter except for a recess 54 which receives a sealing member 56. Turning to Figure 2, the piston 38 cooperates with sealing member 56 and the bore 28 to substantially define an auxiliary chamber 60. The portion of the bore 28 surrounding. auxiliary chamber 60 has the same diameter as its remaining portion. A first passage 62 within the piston 38 includes a first check valve 64 adjacent a threaded bore 66 which receives a stem 68. The stem is cut out at 70 to enable the first passage 62 to communicate with the primary chamber 42. A second passage 72 intersects the first passage 62 and opens to the bore 28 on the side of sealing member 56 opposite auxiliary chamber 60. The second passage 72 could also open to the bore at the sealing member 56 provided the passage 72 terminates at a location to the left of the inner right lip 74 of sealing member 56. A second check valve 76 is disposed within passage 72 and its associated spring is stronger than the associated spring of check valve 64 so that check valve 64 will always open before check valve if both check valves are exposed to the same pressure. The sealing member 56 is substantially X-shaped with a plurality of tabs 7 projecting from the radially outer lips 80 and 86. The plurality of tabs 78 on lip 80 abut the wall of recess 54 to form an aperture 82 communicating the bore 28 with the reservoir 26 via opening 36. The plurality of tabs 78 on lip 86 permit fluid communication from a chamber 79 to auxiliary chamber 60 when braking is terminated and the piston is returning toward snap ring 52 ; however, during movement of the piston toward the left, the pressur developed within chamber 60 causes the lip 86 to deform itself resiliently an tightly engage the top wall of recess 54, thus blocking fluid communication from chamber 60 to opening 36. In addition, the piston 38 is recessed at 84 to open communication between the auxiliary chamber 60 and the reservoir via recess 84, aperture 82 and opening 36, when the piston is abutting snap ring 52. As the axial length of the recesses 84 is only slightly larger than the Axial length of sealing member 56, movement of the piston 38 toward the primary chamber 42 will close the recesses 84 from the auxiliary chamber after a slight amount of pistol movement. The above described device operates as follows When the brake pedal 10 is actuated, the input rod 14 and piston 38 are moved to the left, viewing Figure 2, to contract the volume of fluid within auxiliary chamber 60. Initial movement ofthepiston to the left relative to the sealing member 56 causes fluid within the auxiliary chamber to flc to reservoir 26 via recesses 84, chamber 79, aperture 82 and opening 36. Con- sequently, a small portion of the fluid in auxiliary chamber 60 may be bled tc the reservoir or to the chamber 79 upon initial movement of the piston 38. Further movement of the piston closes the recesses 84 at lip 74 te increase fluid pressure within auxiliary chamber 60 as well as in primary chamber 42. The increased pressure within auxiliary chamber 60 is communicated via passage 62 to check valve 64 to offset the pressure acting against the check valve from primary chamber 42 plus the associated spring of check valve 64 so as to open check valve 64.. Thereafter, increasing fluid pressure within auxiliary chamber 60 is communicated to the primary chamber 42 until a predetermined pressure level is reached in the primary chamber or passage 62. hen the predetermined pressure level is reached, check valve 76 is cpened to vent the aux liary chamber to the reservoir via aperture 82 and opening 36. The increased fluid pressure communicated to the priory chamber cooperates with the ccntraction of spring 50 to move secondary piston 40 so as to pressurize fluid within secondary chamber 46. Consequently, fluid pressure within the primary and secondary chambers is communicated via conduits 20 and 22 to respective brake assemblies 16 and 18 to effectuate braking. Upon termination of braking, the springs 48 and 50 bias the pistons 40 and 38 to return to their rest positions. Primary piston 38 moves re native to the sealing member 56 so as to expand the auxiliary chamber 60 to decrease the pressure therein and to contract chamber 79. As a result fluid from the reservoir 26 and from the chamber 79 flows past right outer lip 86 to replenish fluid within auxiliary chamber 60. Fluid from chamber 79 passes aperture 82 and opening 36 to communicate with reservoir 26 or auxiliary chamber 60 via lip 86. When the primary piston returns to abut snap ring 52, the auxiliary chamber is opened to the reservoir via recesses 84 and aperture 82. In a first alternate embodiment shown in Figure 3, the primary piston 38 includes a first diameter portion 110 and a second diameter portion 112.large in diameter than the first diameter portion 110. The portions are separated by a ramp 114 and the sealing member 56 is engageable with the first diameter portion when the piston 38 is in the rest position. A clearance is established between the bottom wall 116 of recess 54 and the sealing member 56 when the latter is engageable with the first diameter portion to open communication between the reservoir 26 and the auxiliary chamber 60. When the piston 38 is moved to the left during a braking application, the ramp 114 cauls' the sealing member to expand to engage the bottom wall 116. During expansion of the resilient member, a small mount of fluid within auxiliary chamber 60 is bled to reservoir. When the sealing member is expanded by the ramp 114 to movably engage the second diameter portion 112, the sealing member engages the bottom wall 116 to seal the auxiliary chamber from the reservoir 26. Consequently, increasing pressurized fluid within auxiliary chamber 60 is communicated to the primary chamber 42 via passage 62 in the same manner as described above. In a second alternate embodiment shown in Figure 4, a metering valve assembly 210 is disposed between the auxiliary chamber 60 and the primary chamber 42. The metering valve is responsive to fluid pressure within the primary chamber to maintain the auxiliary chamber open to the reservoir 26 when the pressure level in the primary chamber is above a predetermined value. In addition, the metering valve gradually relieves the fluid pressure within the auxiliary chamber to communicate the same to the reservoir, rather than dumping the auxiliary chamber to the reservoir at the predetermined pressure level. This metering valve operates as follows : As the fluid pressure within chamber 42 increases, the metering valve 210 is movable downward to open passage 62 to the recess 54, whereupon fluid pressure is reduced within auxiliary chamber 60. This reduction in fluid pressure at chamber 60 and across the top end of metering valve 210 permits the latter to shuttle upward to close passage 62 to'recess 54 thereby slightly building pressure within passage 62 and chamber 60 to again bias the metering valve downward to open passage 62 to recess 54. Consequently, the fluid pressure within chamber 60 is gradually reduced until the fluid pressure within chamber 42 is sufficient to bias the metering valve to an open position against its spring. Thereafter, the chamber 60 is maintained in communication with the reservoir via passage 62 and recess 54 so long as the fluid pressure within the chamber 42 is above a predetermined level. With respect to all of the embodiments, thbore 28 is substantially uniform in diameter between the primary chamber and the auxiliary chamber and the sealing member 56 is fixed axially within the recess 54. Consequently, the primary piston is movable relative to the sealing member to communicate fluid ressure within the auxiliary chamber to the primary chamber.

Claims: CLAIMS 1. A fast-fill master cylinder comprising a housing defining a fluid reservoir and a bore for movably receiving at least one piston which cooperates therewith to define a primary chamber and an auxiliary chamber both communicating with said reservoir in a rest or brake release position of said one piston, said one piston being movable within said bore to develop fluid pressure within said primary and auxiliary chambers during a braking application and carrying valve means responsive to the fluid pressure built up within said chambers to control fluid communication between the auxiliary chamber and either the primary chamber or the reservoir, said auxiliary chamber being defined between a recessed portion of said piston, the inner wall of the bore and a resilient sealing member held in a fixed axial position with respect to said bore and designed so as to permit fluid communication between the auxiliary chamber and the reservoir when the piston is in its-rest position and to block said communication upon initial movement of the piston from this position, characterized in that said resilient sealing member (56) is held in a recessed portion (54) of the housing bore (28) formed between two bore sections of substantially same diameter, and divides the volume between the recessed portion of the piston (38) and the housing bore (28) into two variable volume chambers, namely the proper auxiliary chamber (60) and a further chamber (79) which is permanently communicated with the reservoir (26). 2. A fast-fill master cylinder according to claim 1, characterized in that the recessed portion of the housing bore consists of an annular groove (54) of substantially rectangular cross-section the bottom wall of which communicates with the reservoir (26), and in that the resilient sealing member (56) is substantially X-shaped in cross-section and includes a first pair of opposite lips (80, 86) engaging the lateral faces of said annular groove (54) and a second pair of opposite lips engaging the bottom wall of the recessed portion of the piston (38). 3. A fast-fill master cylinder according to claim 2, characterized in that the lips (80, 86) of the first pair are each provided with circumferentially spaced tabs (78) which define apertures (82) for fluid communication between the reservoir (26) and said further (79) and auxiliary (60) chambers respectively. 4. A fast-fill master cylinder according to any of claims 1-3, characterized in that the bottom wall of the recessed portion of the piston (38) is stepped to define a first diameter section (110) and a second, laxer diameter section (112), and in that said resilient sealing member (56) normally engages with its second pair of lips said first diameter section and is expandible to engage said second diameter section as the piston is moved during a braking application. 5. A fast-fill master cylinder according to claim 4, characterized in that the resilient sealing member (56) normally defines a radial clearance with the bottom wall (116) of the recessed portion (54) of the bore when engaging said first diameter section (110) of the piston (38), and is brought into engagement with said bottom wall (116) when engaging said second diameter section (112) of the piston.

Inventors: GAISER, ROBERT FRANK
Applicants: THE BENDIX CORPORATION
Application year: 1980
Main classification: B60T11
IPC codes: B60T11