Master cylinder

A master cylinder includes a hydraulic pressure control valve having a valve member mounted in a valve body and normally held apart from a valve seat by a valve spring. The valve member is seated on the valve seat when a pressure in a pressure chamber of a housing of the master cylinder reaches a predetermined level. A control device includes a body received in the bore and having one end portion of a convex shape. The body of the control device is urged by a spring in such a manner that the one end portion projects through a port of the housing into the pressure chamber. The control device including a seat prevention mechanism operatively associating the body of the control device with the valve member so as to prevent the valve member from seating on the valve seat when upon movement of the cylinder piston beyond a predetermined stroke, the cylinder piston engages the one end portion and urges the body of the control device toward the valve member in a direction perpendicular to the axis of movement of the cylinder piston.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a master cylinder for a brake and 
particularly to a hydraulic pressure control valve which is connected to 
an outlet port of the master cylinder and releases its hydraulic pressure 
control operation when a secondary piston of the master cylinder is moved 
excessively beyond a predetermined stroke. 
2. Prior Art 
FIG. 1 shows one conventional hydraulic pressure control valve of this type 
as disclosed in European Patent Application No. 0157158. The hydraulic 
pressure control valve comprises a body 16 mounted at one end in a bore 14 
of a housing of a tandem master cylinder, the bore 14 communicating with a 
pressure chamber 12 defined by the housing and a piston 10. The body 16 
has a bore 18 of a stepped shape in communication with the bore 14, and an 
outlet 20 disposed at the other end of the body 16 and communicating with 
the bore 18. A piston 24 of a stepped shape is slidably received in the 
bore 18 so as to receive a pressure in the outlet 20, the piston 24 having 
a central passage 22 extending therethrough. A preload spring 26 is 
mounted in the bore 18 so as to urge the stepped piston 24 toward the 
outlet 20. A valve member 30 is provided so as to seat on a valve seat 24a 
formed on one end of the stepped piston 24 closer to the bore 14, the 
central passage 22 opening to this one end of the stepped piston 24 The 
valve member 30 is normally held in a predetermined position away from the 
valve seat 24a by means of a valve spring 28. With this hydraulic pressure 
control valve, the stepped piston 24 is held by the preload spring 26 in 
the position shown in FIG. 1 until the hydraulic pressure in the pressure 
chamber 12 reaches a predetermined level, so that the valve member 30 is 
held away from the valve seat 24a. When the hydraulic pressure in the 
pressure chamber 12 exceeds the predetermined level, the stepped piston 24 
is moved upwardly (FIG. 1) against the bias of the preload spring 26, due 
to the hydraulic pressure differential between the greater diameter 
portion 24b and smaller diameter portion 24c of the stepped piston 24. As 
a result, the valve seat 24a is brought into seating engagement with a 
lower portion 30a of the valve member 30. Therefore, the rate of increase 
of the hydraulic pressure leading to the outlet 20 and acting on a brake 
for rear wheels of the vehicle becomes smaller than that of the hydraulic 
pressure (which is the same as the hydraulic pressure for a brake for the 
front wheels) in the pressure chamber 12. 
However, if such a pressure control is carried out even when a brake 
circuit for the front wheels is subjected to malfunction, braking forces 
are insufficient to brake the vehicle. For this reason, with the hydraulic 
pressure control valve shown in FIG. 1, when the piston 10 is moved 
excessively beyond a predetermined stroke, a flange 10a of the piston 10 
is brought into engagement with an upper portion 30b of the valve member 
30 to move the valve member 30 in a direction perpendicular to the axis of 
the valve member 30 so as to pivot the valve member about its lower end 
30c, thereby preventing the valve member 30 from seating on the valve seat 
24a. 
With the conventional hydraulic pressure control valve of FIG. 1, however, 
in the event of the replacement of component parts or the like, the piston 
10 can not be removed from the housing of the master cylinder without 
removal of the hydraulic pressure control valve from the master cylinder 
housing since the valve member 30 extends into the pressure chamber 12. 
SUMMARY OF THE INVENTION 
It is therefore an object of this invention to provide a master cylinder in 
which the piston of the master cylinder can be removed from the master 
cylinder housing without removal of the hydraulic pressure control valve 
from the housing. 
According to the present invention, there is provided a master cylinder 
comprising: 
(a) a housing having a pressure chamber; 
(b) a cylinder piston received in said housing and being normally movable 
over a predetermined stroke along an axis; and 
(c) a hydraulic pressure control valve comprising (i) a hollow body 
attached to said housing and having a bore at one end and an outlet at the 
other end, said housing having a port communicating said pressure chamber 
with said bore, (ii) a valve piston received in said body for movement, 
said piston having a passage, said pressure chamber being in communication 
with said outlet via said bore and said passage, said valve piston having 
a valve seat at one end disposed adjacent to said bore, said passage 
opening to said valve seat, (iii) a valve member mounted in said bore and 
normally held apart from said valve seat by a valve spring, said valve 
member being seated on said valve seat when the pressure in the pressure 
chamber reaches a predetermined level, and (iv) a control means comprising 
a body received in said bore and having one end portion of a convex shape, 
said body of said control means being urged by a spring in such a manner 
that said one end portion projects through said port into said pressure 
chamber, said control means including seat prevention means operatively 
associating said body of said control means with said valve member so as 
to prevent said valve member from seating on said valve seat when upon 
movement of said cylinder piston beyond said predetermined stroke, said 
cylinder piston engages said one end portion and urges said body of said 
control means toward said valve member in a direction perpendicular to the 
axis of movement of said cylinder piston.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
The invention will now be described with reference to the drawings in which 
like reference numerals denote corresponding parts in several views. 
A tandem master cylinder shown in FIG. 2 comprises a housing or body 70 
having an annular hollow boss 72. The boss 72 has internal threads 72a 
formed in an inner surface thereof. The housing 70 has a port 74 
communicating the interior of the housing 70 with the interior of the boss 
72. The boss serves as a mounting portion for supporting a hydraulic 
pressure control valve 80. 
A body 16 of the hydraulic pressure control valve 80 comprises a pair of 
first and second members 16a and 16b threadedly connected together. The 
first member 16a is threaded into the boss 72 at one end thereof, and the 
second member 16b has an outlet 20 at one end thereof. A piston 24 of a 
stepped shape is received in the body 16, and a preload spring 26 acts on 
the piston 24 to hold an intermediate flange 24d of the piston 24 against 
a shoulder 16c of the second body member 16b. Thus, the piston 24 is 
normally held stationary. In this condition, a valve seat 24a, formed on 
one end of the piston 24 to which a central axial passage 22 opens, is 
disposed immediately adjacent to a bore 76 formed in an upper end of the 
first member 16a. A valve member 50 of the poppet type is received in the 
bore 76. The valve member 50 has a bullet-shaped body 52, a cylindrical or 
tubular portion 54 surrounding the body 52 in coaxial relation thereto, 
and a connective wall 56 interconnecting the body 52 and the cylindrical 
portion 54. A plurality of, for example, three apertures 58 is formed 
through the connective wall 56 and are circumferentially spaced from one 
another. The valve 50 is urged by a valve spring 28 in such a manner that 
the lower end of the cylindrical wall 54 is held against a shoulder 16d, 
i.e., the bottom of the bore 76. In this condition, the lower end of the 
valve body 52 is spaced slightly from the valve seat 24a. Therefore, in 
the illustrated condition of the hydraulic pressure control valve 80, a 
pressure chamber 12, defined by the housing 70 of the master cylinder and 
a piston 10, is in communication with the outlet 20 via a port 74 formed 
in the housing 70, the apertures 58 and the central passage 22 of the 
piston 24. The piston 10 is received in the housing 70 for sliding 
movement along an axis of the piston 10. 
A control member 60 includes a body 62 defined by a hollow cylindrical head 
portion 62a and a flat peripheral flange formed around the lower end of 
the head portion 62a, and three pawls 64 extending downwardly away from 
the head portion 62a. The pawls 64 extends through the apertures 58 of the 
valve member 50, respectively, and are directed toward the lower end of 
the valve body 52, so that the lower ends 64a of the pawls 64 are disposed 
adjacent to the lower end of the valve body 52. In the case where the 
control member 60 is molded from a plastics material, it is preferred that 
the pawls 64 should be resiliently engaged slightly with the peripheral 
surface of the valve body 52. The valve spring 28 is received in the 
hollow head portion 62a of the control member 60, so that the flange of 
the control member 60 is urged by the valve spring 28 against the surface 
of the housing 70 disposed around the edge of the port 74. In this 
condition, the head portion 62a of the control member 60 extends through 
the port 74 in spaced relation thereto, and an upper end of the head 
portion 62a projects slightly into the pressure chamber 12. The upper end 
of the head portion 62a is convex and more specifically semi-spherical or 
rounded, and the intersection P between the rounded end surface of this 
upper end and the peripheral surface of the head portion 62a is disposed 
either in a plane in which the upper edge of the port 74 lies (that is, in 
a plane of the inner surface of the wall of the housing 70 through which 
the port 74 is formed) or disposed slightly below this inner surface of 
the housing wall. With this arrangement, flanges 10a and 10b formed on the 
piston 10 can smoothly engage with the rounded upper end of the head 
portion 62a. 
When a brake circuit for front wheels is subjected to malfunction, the 
piston 10 is axially moved excessively beyond a predetermined stroke, so 
that the flange 10a of the piston 10 is brought into engagement with the 
rounded head portion 62a to urge the control member 60 downwardly toward 
the valve member 50 against the bias of the valve spring 28, so that the 
control member 60 is moved along the axis of the valve member 50, that is, 
in a direction perpendicular to the axis of movement of the cylinder 
piston 10. It will be appreciated that the amount of movement of the 
control member 60 is determined by the amount of projection of the head 
portion 62a into the pressure chamber 12. Upon downward movement of the 
control member 60 along the axis of the valve member 50, the lower ends 
64a of the pawls 64 of the control member 60 are moved to be interposed 
between the valve body 52 and the valve seat 24a of the piston 24 so as to 
prevent 60 the valve member 50 from seating on the valve seat 24a , 
thereby maintaining the communication between the pressure chamber 12 and 
the outlet 20. 
When the piston 10 is removed from the housing 70 of the master cylinder, 
this can be easily effected without removal of the hydraulic pressure 
control valve 80 from the housing 70 since the control member 60 is 
smoothly retracted toward the valve member 50 upon engagement with the 
piston 10. In addition, when assembling the hydraulic pressure control 
valve 80, since the control member 60 has the pawls 64, the control member 
60, the valve spring 28 and the valve member 50 can be assembled much like 
a unit, so that the assembly of the hydraulic pressure control valve 80 
can be carried out easily. 
FIG. 3 shows a modified hydraulic pressure control valve 80a. A control 
member 60a has a hollow cylindrical head portion 62b, a hollow cylindrical 
portion 64b of a greater diameter and an annular flat connective portion 
61 interconnecting the head portion 62b and the cylindrical portion 64b. 
The head portion 62b has a port 62c formed through its upper end, and is 
tapered or rounded. An annular base member 90 is received in the bore 76 
of the first member 16a and rests on the shoulder 16d. An upper end of the 
annular base member 90 is formed into an annular ridge 91. A deformable 
support ring 92 is mounted around a valve member 50a and has four radially 
outwardly-extending arms 93 of a resilient nature, as best shown in FIG. 
4. The resilient arms 93 rest on the ridge 91 of the base member 90 at one 
side thereof. The cylindrical portion 64b is disposed around the annular 
ridge 91. The lower end of the cylindrical portion 64b of the control 
member 60a engages the outer ends of the four resilient arms 93 of the 
support ring 92 at the other sides of the arms 93. A valve spring 28a acts 
between the control member 60a and the valve member 50a. When the flange 
10a of the piston 10 engages the head portion 62b to urge the control 
member 60a downwardly toward the valve member 50b, the four arms 93 of the 
support ring 92 are deformed or pivotally moved by the cylindrical portion 
64b about the annular ridge 91 of the annular base member 90, so that the 
support ring 92 is moved upwardly together with the valve member 50a, 
thereby preventing the valve member 50a from seating on the valve seat 
24a. A peripheral wedge-shaped projection 95 is formed around the outer 
surface of the cylindrical portion 64b of the control member 60a. The 
projection 95 is engaged with an inwardly-directed upper end of the first 
member 16a when the control member 60a is mounted on the first member 16a, 
thereby preventing the control member 60a from disengaging from the first 
member 16a when attaching the hydraulic pressure control valve 80a to the 
housing 70 of the master cylinder. The stroke of the valve member 50a can 
be suitably determined by changing the diameter of the annular ridge 91. 
FIG. 5 shows a modified control member 60b which has a head portion 100 
loosely received in the port 74, the head portion 100 having a transverse 
passage 102 extending therethrough and an axial passage 104 leading from 
the transverse passage 102 to the lower surface of the head portion 100.