FR2492756A1 - MASTER CYLINDER FOR HYDRAULIC BRAKE SYSTEM - Google Patents

Abstract

THE INVENTION RELATES TO A MASTER CYLINDER. ACCORDING TO THE INVENTION, IT INCLUDES A STEP BORE CONSISTING OF SMALL DIAMETER 1B AND LARGE DIAMETER 1A CYLINDERS, A STEP 2 PISTON CONSISTING OF SMALL DIAMETER PISTONS 2B IN CYLINDER 1B DEFINING A PRESSURE CHAMBER 12 THEREIN LARGE DIAMETER 2A IN CYLINDER 1A Y DEFINING A CHARGING CHAMBER 11, A SECTIONAL JOINT 10 ON PISTON 2B ALLOWING FLUID TO FLOW FROM CHAMBER 11 TO CHAMBER 12, A TANK 16, A RELIEF VALVE 31 IN A PASSAGE CONNECTING THE RESERVOIR TO CHAMBER 11 AND HAVING A PORT 33, THIS VALVE HAVING A BODY 42, SOLICITED BY A BLADE SPRING 43, WHICH OPENS WHEN THE PRESSURE IN CHAMBER 11 EXCEEDS A FIRST PREDETERMINED VALUE AND A VALVE SUPPLY 31 BETWEEN THE TANK AND CHAMBER 11 TO DELIVER FLUID THERE WHEN THE PRESSURE DECREASES BELOW A SECOND PREDETERMINED VALUE, LOWER THAN THE FIRST. THE INVENTION APPLIES IN PARTICULAR TO THE BRAKING OF MOTOR VEHICLES.

Description

The present invention relates to a master cylinder for use in a

  hydraulic braking system and in particular, to master cylinders of the type that can bring a large amount of a fluid at relatively low pressure in the initial stage of the application of the brake and bring a small amount of a fluid at high pressure

  at the remaining stage of application of the brake.

  A prior art master cylinder of the aforementioned type comprises a stepped bore consisting of a small diameter cylinder and a large diameter cylinder, a stepped piston consisting of a small diameter piston working in the small diameter cylinder. to set a room for putting under

  displacement pressure of a small volume and at a high pressure

  a large-diameter piston operating in the large-diameter cylinder to define a high-volume, low-pressure displacement charging chamber; a reservoir for supplying fluid from the delivery chamber;

  under pressure at the charging chamber, a valve of

  provided between the charging chamber and the reservoir to allow fluid flow from the charge chamber to the reservoir when the pressure in that charging chamber exceeds a first predetermined pressure, and a supply valve provided between the reservoir and the charging chamber for allowing the flow of fluid from the reservoir to the charging chamber when the pressure in this charging chamber decreases below a second pressure

  predetermined, less than the first pressure.

  The expansion valve comprises a body defining a passageway therethrough and having a seat and a orofice or a restricted surface portion, a valve member such as a ball cooperating with the seat and a coil spring acting on the valve to the closing direction of the valve Thus, this has a drawback because the expansion valve produces noises or noisy vibrations when it opens. It can be considered that the reasons for this lie in the fact that the deflection of the coil spring changes linearly with the change of the load, so that the valve member can not separate sufficiently from its seat when the pressure is not sufficiently larger than the opening pressure of the valve, and 1 t valve member tends to open and close the valve oscillatingly because the static pressure that acts on the valve member to open it changes in response to the flow that passes through the valve. Furthermore, the orifice of the expansion valve according to the prior art is provided downstream of the valve member and the fluid that passes through the orifice enters directly into the tank at an increased speed when a large volume amount of fluid passes through the expansion valve causing noises. When the master cylinder is installed on a vehicle, these noises or vibrations are transmitted to the

  vehicle, which is dangerous and uncomfortable.

  The present invention aims to overcome the

  disadvantages above master cylinder according to the prior art

  in order to suppress noise or vibrations produced

  by the mechanism of the expansion valve.

  The present invention relates to a master cylinder of the type comprising a stepped bore consisting of a small diameter cylinder and a large diameter cylinder, a stepped piston consisting of a small diameter piston working in the cylinder. a small diameter for defining a low volume, high pressure displacement pressurization chamber, and a large diameter piston operating in the large diameter cylinder to define a high volume, low pressure displacement charge chamber, means provided between the charge chamber and the pressurizing chamber to allow the flow of fluid from the charge chamber to the pressurizing chamber when the pressure in the first is greater than that in the second, a reservoir of fluid for supplying fluid to both chambers, an expansion valve provided in a passage connecting the reservoir to the charging chamber and having a spring loaded valve member which opens when the pressure in the charging chamber exceeds a first value predetermined, an orifice provided in the passage of the expansion valve and a feed valve provided between the reservoir and the charge chamber e to allow the flow of fluid from the reservoir to the charge chamber when the pressure in the chamber of

  charge decreases below a second predetermined value.

  minus the first, and according to the inventiox: the valve member of the expansion valve is biased by a leaf spring traversed by an opening and by this

  opening flows2e fluid passing through the expansion valve.

  Preferably, the orifice of the expansion valve

  is provided upstream of the valve member.

  The invention will be better understood, and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory text which follows, with reference to pliers deins illustrating several embodiments and in which: - Figure 1 is a longitudinal sectional view of a tandem master cylinder according to the invention; Figure 2 is an enlarged view showing the essential portion of Figure 1; FIG. 3 is an enlarged, plan view of a cup-shaped leaf spring which is incorporated in the master cylinder of FIG. 1; - Figure 4 is a plan view similar to Figure 3 but showing a modified form; and - Figure 5 is a load-deflection diagram

  a coil spring (A) and a leaf spring (B).

  Fig. 1 shows a tandem reservoir and master cylinder assembly used in a vehicle hydraulic hoisting system, which comprises a main body 1 defining a stepped bore consisting of a large diameter cylinder 1A and a small cylinder 1B. diameter. The main body further comprises boss portions 1C and 1D o is mounted a tank 16. A primary piston 2 consisting of a large diameter piston 2A and a small diameter piston 2B works in the stepped bore and a secondary piston 3 works in the small diameter cylinder 1B and in front of the primary piston; a rod 4 is attached to the inner end or front of the primary piston 2, and it.is protruding, and this rod4

  slidably engages a restraint means 5 generally

  in the form of a cap, which is normally abutting with the rear end of the secondary piston 3 by means of a return spring 7. The return spring 7 extends between the retaining means 5 and a retaining means 6 of the which spring is attached to the primary piston 2. Furthermore, a return spring 9 for the secondary piston 3 extends between the inner end of the cylinder 1 B of small diameter and a retaining means 8 mounted on the inner end part.

of the secondary piston 3.

  A primary seal in section 10 is mounted on the piston 2B of small diameter of the primary piston 2. The flow allows the flow of the liquid only a chamber of

  load 11 which is defined at the front of the large diameter piston

  meter 2A to a pressurizing chamber 12 which is defined at the front of the small diameter piston 2B. For the actuation of the master cylinder, the charge chamber It moves a large volume at a relatively low pressure while the pressurizing chamber 12 can produce

  a high pressure with a displacement of a small volume.

  A secondary seal in section 13, similar to the primary seal 10, is mounted on the secondary piston 3 and separates a pressurizing chamber 15 from a charging chamber 14. The flow of the liquid passing through the seal 13 of the the charging chamber 14 to the pressurizing chamber 15 occurs only during the return stroke of the master cylinder, however, the primary seal 10 further allows the flow of liquid from the charging chamber 11 to the delivery chamber. under pressure 12 at the initial stage of the actuation stroke of the master cylinder,

what will be explained below.

  The reservoir 16 is sealingly mounted on the boss portions 1C and 1D of the Main Body 1 by seals 17. The reservoir 16 is connected to the charging chambers 11 and 14 by feed passages 18 and 19 respectively, and it is connected to the slot rooms

  pressure 12 and 15 through expansion ports 20 and 21 ,.

  respectively at the non-actuated condition of the master cylinder as can be seen in Fig. 1. In 22 and 23 are shown, for example, connected outlets

  to the wheel cylinders (not shown).

  The tandem master cylinder shown in the drawings is actuated for example by depressing a brake pedal (not shown), and pressurized liquid is supplied from the outlet ports to the respective cylinders.

  wheels, however, the present invention is not limited to

  tandem master cylinders and can be applied to single cylinder marten, o the secondary piston 3 and the

parts thereof are omitted.

  The essential part of the invention is

  Figure 31 shows a valve assembly constituting the essential part of the invention which comprises an annular vanilla body 32 fixed

  in the boss 1C of the main body.

  33 is formed along the central tax of the valve body 32, and the upper portion of the orifice 33 is counter-bored to form a valve seat 34 with which cooperates a ball acting as a valve member. In the valve seat 34 is provided a cutout 35 defining a tiny passing surface. Thus, the tank 16 and the load chamber 11 are in permanent communication through the cutout 35, the orifice 33 and the passage 18. The ball 42 is normally

  biased against the valve seat 34 by an onnu-

  laireàlam-43 in the shape of a section. The ball 42, the spring 43, the valve seat 34 and the orifice 33 constitute an expansion valve, and the orifice 33 determines the maximum flow.

  which can go through the expansion valve.

  The valve body 32 further comprises a number of angularly spaced feed passages

  36 which surround the orifice 33. The passages 36 are normal

  The seal 38 engages the inner circumferential surface of the boss 1C and the

  outer circumferential surface of the valve body 32.

  In this embodiment, the seal 38 is secured in an annular groove 37 in the outer circumference of the valve body 32 and the lip 38A extends radially inwardly. When the pressure in the charging chamber 11 decreases below the atmospheric pressure or the pressure in the reservoir 16, the lip 38A deforms downwards and the liquid in the reservoir is

  brought to the load chamber 11 by the passages 36.

  A cap 39 having a protruding center portion 39A and a skirt forming portion 39B covers the upper end of the valve body 32 and retaining the outer circumference of the spring 436. A plurality of openings are provided in the side wall of the protuberance portion 39A. . The skirt portion 39B of the cap 39 is attached to the upper end of the valve body 32 by force adjustment, matting or the like. The cap 39, the spring 43, the ball 42, the valve body 32, and the seal 38 constitute a set of expansion valve and supply valve which is fixed in the circumference

  the boss 1C and is held there by a retaining ring

naked 41.

  The spring-43 has, as can be seen in Figure 3, a number of radially extending slots 44A, which serve as the flow passage of the liquid flowing through the expansion valve. Slots 44A may be replaced by spaced holes 44B, as can be seen in FIG.

figure 4.

  FIGS. 1 and 2 show the non-actuated condition of the master cylinder, in fact the clearance between the primary piston 2 and the secondary piston 3 is defined by the engagement between the retaining means 5 and the head portion of the rod 4 due to the fact that return spring 7, and the outer end of the primary piston 2 engages a stop 24 due to the return spring 9 (note that the spring 7 is stronger than the spring 9). Furthermore, the ball 42 engages the valve seat 34 to close the

  valve, and the lip 38A closes the valve

  However, the reservoir 16 communicates with the charge chamber 11 through the cutout 35 formed in the valve seat 34. The pressure chamber 12 also communicates with

the tank 16.

  When the brake pedal is depressed, the primary piston 2 moves to the left in FIG. 2, and the liquid in the large cylinder 1A is compressed by the surface difference between the large diameter cylinder 1A and the small diameter cylinder 1B. The pressurized liquid that occurs in the charging chamber 11 is fed into the pressurizing chamber 12 through the supply port 18 and the expansion port 20 until the sectional seal 10 provided on the small diameter piston 2B closes the expansion orifice 20. Next,

  when the pressure in the charging chamber is greater than

  greater than the pressure in the pressurizing chamber 12, the liquid in the chamber flows into the chamber 12

  by deformation of the joint in section 10.

  It should be noted that the piston 2B of small diameter serves to compress the liquid in the chamber of putting under

  pressure 12, however when the wheel cylinders require

  a large amount of liquid at the initial stage of application of the brake for reasons such as the brake clearance is relatively large and the effective surface and the stroke of the small diameter piston 2B are small in comparison with those of the cylinders of the brake. wheels, the pressure in chamber 12 does not increase until

  that the play of the brake has been compensated.

  The liquid in the charging chamber 11 also flows into the reservoir 16 through the feed orifice 18, the orifice 33, the cutout 35 and the passages 40, however the passage area of the cutout 35 is so small a

  sufficient pressure occurs in the charging chamber 11.

  When the play of the brake has been compensated, the small diameter piston 2B pressurizes the liquid into the chamber 12, and the liquid in the charging chamber 11 is not brought into the pressurizing chamber 12, and the liquid in the charging chamber 11 is not brought into the pressurizing chamber 12, after this stage,

  the pressure in the chamber 11 is ineffective for the application

  brake and constitutes a loss in the application force of the brake. When the pressure in the charging chamber 11 increases to a predetermined level, the ball 42 of the expansion valve rises against the biasing force of the spring 43. As can be seen in Figure 5, the spring deflection With blade 43 relative to the load is very important in comparison to conventional coil springs, so the ball 42 can sufficiently separate from the valve seat and it is possible to pocket the oscillating movement of the valve member relative to the seat which was observed in a usual valve member urged by a coil spring. As a result, it is possible to avoid vibration noises. The orifice 33 is provided upstream of the ball 42 and defines the maximum flow that passes through the expansion valve and additionally 7 even if the large diameter piston 2A advances rapidly, the pressure acting on the ball 42 does not change. abruptly according to

  the flow resistance of the orifice 33, and the function

  the regular and reliable dentening valve. On the other hand, the liquid that passes through the expansion valve passes through passages 44A in the leaf spring 43 and the passages 40.

  in the cap 39 and is thus depreciated, thereby

  the noise produced in the liquid through

  the orifice 33 can be sufficiently damped or dissipated.

  The passages 40 are formed in the side wall of the protuberance portion 39A, thus the liquid flowing through the passages 44 does not impact the wall

upper tank 16.

  When the depressing force of the brake pedal is released, the primary piston 2 returns or moves to the right in the drawings thanks to the force of the return spring 7, and the volume of the charging chamber 11 increases and the pressure decreases. When the pressure in the charging chamber 11 has fallen below a predetermined value, the annular lip 38A deflects downwards to open the passages 38. The liquid in the reservoir 16 is fed into the charging chamber 11 through

  passages 40 and 44A and passages 38.

  The master cylinder according to the invention having the construction described above has the following advantages: a) The valve member of the expansion valve jr is biased by a leaf spring 43 in the form of a cup, so in comparison with valves having a coil spring for biasing the valve member, it is possible to sufficiently separate the valve member 42 from its seat 34, thereby preventing vibration noise caused by the

  Self-excited vibration motion of the valve member.

  b) The orifice 33 is provided upstream of the valve member 42 of the expansion valve, thus, the expansion valve can not open accidentally and its operation is

regular and reliable.

  c) The liquid passing through the orifice 33 produces significant noise, however, it then passes into the restricted passages 44A of the leaf spring 43 and the restricted passages 40 of the cap 39, damping and

dissipating the noises.

Claims (3)

R E V E N D I C A T I 0 N S   A master cylinder characterized by comprising a stepped bore consisting of a small diameter cylinder (1B) and a large diameter cylinder (1A), a stepped piston (2) consisting of a small diameter piston (2B) working in the small diameter cylinder   to define a pressurizing chamber (12) to be moved   low volume and high pressure piston and a large diameter piston (2A) operating in the large diameter cylinder to define a high volume, low pressure displacement charge chamber (11), a sectional joint (10), ) mounted on the small diameter piston and allowing fluid flow only from the charge chamber to the pressurizing chamber, a reservoir (16) for supplying fluid to the pressurizing chamber and the pressure chamber. charge, an expansion valve (31) provided in a passage connecting the reservoir to the charging chamber and having an orifice (33), said expansion valve having a spring loaded valve member which opens when the pressure in the charging chamber exceeds a first predetermined value, and a supply valve (31) provided between the reservoir and the charging chamber for supplying fluid into the charging chamber when the pressure in said charging chamber   decreases below a second predetermined value   lower than the first, said spring urging said valve member of said expansion valve being a leaf spring.   2. Master cylinder according to claim 1, characterized in that the aforementioned valve member is a ball (42) and in that the leaf spring (43) above is a ring-shaped annular member, the central portion engages the ball, said spring having a number of angularly spaced openings (44A; 44B), for the flow of liquid passing through said valve; relaxation.   1L1 3. Master cylinder according to claim 1, characterized in that the aforementioned orifice is provided upstream of the aforementioned valve member.