Apparatus for controlling braking liquid pressure

An apparatus for controlling braking liquid pressure produces a proportionate reduction in an input liquid pressure supplied from a master cylinder before it is output to a rear wheel cylinder. The apparatus includes a body which is formed of a single member and which is formed with a bore in which a plunger slides. An annular retainer having an inner diameter less than that of the bore is fitted into the bore at its end nearer the master cylinder. One end of the plunger extends through the annular retainer.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for controlling braking liquid 
pressure which may be used in a braking system of a vehicle to produce a 
proportionate reduction in an input liquid pressure to derive an output 
liquid pressure. 
An apparatus for controlling braking liquid pressure is used in order to 
produce braking efforts of an equal magnitude for both the front and the 
rear wheels during the initial phase of a braking operation when such 
efforts are at their low level, and to reduce the braking effort applied 
to the rear wheels as compared to that applied to the front wheels so that 
both the front and the rear wheels may be locked simultaneously whenever 
the braking effort exceeds a given value. At this end, such apparatus 
includes a plunger which is responsive to the pressure prevailing in a 
master cylinder to open or close a valve, which in turn produces a 
proportionate reduction in the pressure transmitted from the master 
cylinder before it is applied to a rear wheel cylinder. 
In a usual apparatus for controlling braking liquid pressure, a plunger 
used therein has opposite end faces of different areas which are subject 
to respective pressures so as to be operated in accordance with the master 
cylinder pressure which is applied to the both end faces. Accordingly, the 
plunger is slidably disposed within a bore formed in a body. The bore has 
portions of an increased and a reduced diameter, and the portion of the 
increased diameter is closed by a plug in order to contain the plunger 
within the bore. Thus, a combination of the body which contains the 
plunger and the plug is used. However, the combination of the body and the 
plug presents a limit in reducing the size of the profile of the apparatus 
and also poses a problem in that a high accuracy is required in assembly 
and machining to achieve the concentricity between the body and the plug 
since the plunger is disposed in sliding contact with both the body and 
the plug. It is proposed to crimp the plug to the body so as to provide an 
integral construction. With this construction, a torque of an increased 
magnitude is applied to the crimped regions when mounting the apparatus on 
the master cylinder, and also an excessive load is applied to the crimped 
regions during the operation, thus presenting another difficulty that an 
increased strength requirement is imposed upon the crimped regions. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the invention to provide an apparatus for 
controlling braking liquid pressure which is simple and compact in 
construction. This object is achieved by molding a cylindrical body from a 
single member and by fitting a retainer into a bore formed in the body on 
the side nearer the master cylinder, with one end of a plunger projecting 
through the retainer. 
It is another object of the invention to provide an apparatus for 
controlling braking liquid pressure which facilitates its mounting on or 
dismounting from the master cylinder. 
It is a further object of the invention to provide an apparatus for 
controlling braking liquid pressure which eliminates the need for the 
concentricity between the body and the plug and which allows a facilitated 
assembly and machining with a high accuracy. 
Other objects and advantages of the invention will become apparent from the 
following description with reference to the attached drawings.

DESCRIPTION OF EMBODIMENTS 
Referring to FIG. 1, there is shown a body 1 which is molded from a single 
member into substantially cylindrical configuration. A master cylinder 
includes a casing 2 in which a mounting hole 3 is formed, in which the 
body is threadably engaged. The body 1 is formed with an axially extending 
bore, the central portion of which represents a slide bore 5 in which a 
plunger 4 is slidably disposed. A nodule 6 is formed in contiguous 
relationship with the bore 5 and extends radially inward. An output port 7 
for communication with a rear wheel cylinder, not shown, is defined in the 
outer end of the body. An annular retainer 8 having a inner diameter less 
than the inner diameter of the slide bore 5 is fitted into the bore formed 
in the body 1 at its end abutting against the master cylinder. An annular 
seal member 9 is disposed in abutting relationship with the end face of 
the retainer 8 which is opposite from the body 1. The annular retainer is 
mounted in the body 1 by externally crimping a cylindrical end portion 1a 
of the body 1, thus facilitating its assembly. 
The plunger 4 has a portion 4a of an increased diameter which is disposed 
in fitting engagement with the slide bore 5, and also includes a portion 
4b of a reduced diameter which extends toward the master cylinder. The 
free end of the portion 4b extends through the retainer 8 and the seal 
member 9, with its projecting end portion 4c having an end face which is 
located opposite to the bottom surface 3a of the mounting hole 3. The seal 
member 9 is disposed in sliding contact with the portion 4b, of a reduced 
diameter, of the plunger 4 in a liquid tight manner and is also tightly 
fitted against the inner wall of the mounting hole 3, thus preventing any 
leakage of hydraulic oil discharged from the master cylinder to the 
exterior. It will be noted that a snap ring 10 is fitted on a portion of 
the reduced diameter portion 4b which projects beyond the seal member 9 so 
the seal member 9 can be disengaged by the snap ring 10 whenever the body 
1 is removed out of the casing 2. 
A spring 11 is disposed between a step 4d defined between the portions 4a 
and 4b of increased and reduced diameters of the plunger 4 and the 
retainer 8, whereby the plunger 4 is normally urged to the left, as viewed 
in FIG. 1, or toward the nodule 6. As is well recognized, when the plunger 
4 is moved to the right against the resilience of the spring, an output 
liquid pressure from the output port 7 will be reduced as compared with 
the input liquid pressure supplied from the master cylinder. Such 
reduction of the pressure is performed by the action of a valve body 13 
received within a valve chamber 12 which is formed within the increased 
diameter portion 4a of the plunger 4. The valve body 13 is normally urged 
toward the nodule 6 by a spring 14 extending between it and the bottom of 
the valve chamber 12. The valve body 12 has an end 13a of a reduced 
diameter which normally projects through a bore formed in an annular valve 
seat 17 which is fitted into the opening of the valve chamber 13. A disc 
15 is fitted into the opposing end face of the nodule 6 for abutment by 
the end 13a of the valve body 13. The disc 15 is formed with openings 16 
which allow a communication between the valve chamber 12 and the output 
port 7, whereby the hydraulic oil passing through a passage 4e formed in 
alignment with the axis of the plunger 4 can be introduced into the output 
port 7. 
When the apparatus is inoperative, the plunger 4 is urged by the spring 11 
into abutment against the nodule 6 while the valve body 13 abuts against 
the disc 15 and thus is clear from the valve seat 17. Accordingly, the 
hydraulic oil supplied from the master cylinder passes through the passage 
4e, the valve chamber 12 and the openings 16 to be introduced into the 
output port 7 so as to be supplied to the rear wheel cylinder. When the 
input liquid pressure from the master cylinder increases above a given 
value, the plunger 4 is moved to the right against the resilience of the 
spring 11 since the end face of the increased diameter portion 4a has a 
greater area, subject to the liquid pressure, than the area of the end 
face of the projecting end 4c of the plunger 4. It will be seen that such 
rightward movement is limited by the abutment of the projecting end 4c 
against the bottom surface 3a of the mounting hole 3. On the other hand, 
since the valve body 13 is urged by the spring 14, it moves relative to 
the valve seat 17 until it becomes seated on the latter. Thereupon, the 
path for the hydraulic oil to the output port 7 is interrupted, ceasing a 
further increase in the output liquid pressure. As the input liquid 
pressure continues to increase, such liquid pressure causes the plunger 4 
to move to the left, whereby the valve body 13, abutting against the disc 
15, is again moved clear from the valve seat 17, allowing the liquid 
pressure introduced into the output port 7 to increase again. A further 
increase in the liquid pressure causes a movement of the plunger 4 to the 
right as mentioned above. Such process is repeated to produce a 
proportionate reduction of the input liquid pressure to derive an output 
liquid pressure. It is to be understood that during the time the liquid 
pressure supplied to the rear wheel cylinder is controllably reduced by 
the operation described above, the liquid pressure from the master 
cylinder is directly introduced into the front wheel cylinder through an 
output port 18. 
As a result of the described construction, during the assembly operation, 
the valve body 13 is initially inserted into the plunger 4, which is then 
assembled into the body 1. After inserting the spring 11, the retainer 8 
is fitted into the cylindrical end portion 1a of a reduced thickness. The 
cylindrical end portion 1a may then be crimped to secure the retainer 8 in 
place. The seal member 9 is then fitted over the plunger, followed by the 
fitting of the snap ring 10. The integral assembly may be threadably 
engaged with the mounting hole 3 of the casing 2. When an inspection or 
replacement of the apparatus is desired, the body 1 may be removed from 
the mounting hole 3, and then all the components can be disassembled by a 
procedure which is opposite to that mentioned above, thus facilitating the 
required operation. 
In the above description, the retainer 8 has been fixed in place by 
crimping the cylindrical end portion 1a of a reduced thickness. However, 
it should be understood that the crimped region is located outside the 
flow path of the hydraulic oil and hence is not subject to the action of 
the liquid pressure. Accordingly, no increased strength requirement is 
required of the crimped region, which maintains a high reliability over a 
prolonged period of use. It should also be noted that it is unnecessary to 
utilize the crimping to fix the retainer 8, which may be a press fit. 
FIG. 2 shows a second embodiment of the invention which is similar to the 
embodiment mentioned above except for the arrangement associated with a 
retainer. Specifically, a retainer 20 is secured to a cylindrical end 
portion 1a of the body 1 which has a reduced thickness, by crimping. A 
recess 20a is formed around the inner periphery of the retainer 20, and a 
seal member 21 is fitted into the recess 20a. An annular groove 20b is 
formed around the outer periphery of the retainer, and receives an O-ring 
22. Thus, the seal member 21 maintains a liquid tightness between the 
interior of the body 1 and the master cylinder while the O-ring 22 
maintains a liquid tightness between the master cylinder and the exterior. 
This is compared to the first mentioned embodiment in which the seal 
member 9 serves maintaining the liquid tightness for all purposes. This 
represents a structural difference between the both embodiments. In the 
second embodiment, it will be noted that a spring seat 23 is defined 
adjacent to the step 4d formed in the plunger 4, with the spring 11 
extending between the spring seat 23 and the retainer 20. 
The second embodiment operates in the similar manner as the first mentioned 
embodiment, and therefore will not be described. 
While the invention has been shown and described above in terms of several 
embodiments thereof, it should be understood that a variety of changes and 
modifications are possible therein without departing from the spirit and 
scope of the invention as defined by the appended claims.