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Claims  |
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What is claimed is:
1. A tandem type vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss for engaging said front booster piston;
a coupling cylinder extending from an inner peripheral edge of said front
booster piston and positioned in a front end portion of said piston boss,
said coupling cylinder including a bottom plate for coupling with said
piston boss;
a return coil spring elastically set between a front end wall of said
booster shell and said piston boss, for urging said piston boss in a
direction away from said front end of said booster shell; and
a reinforcing cylinder comprising synthetic resin and being positioned in
said coupling cylinder, said coupling cylinder integrally formed with said
front booster piston,
wherein said reinforcing cylinder includes an inward flange at a front end
thereof for reinforcing said reinforcing cylinder and for holding said
return coil spring, said inward flange being biased by a rear end of said
return coil spring for holding said reinforcing cylinder on said bottom
plate of said coupling cylinder at a predetermined contact position, said
reinforcing cylinder being held solely by said return coil spring.
2. A tandem type vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss for engaging said front booster piston;
a coupling cylinder extending from an inner peripheral edge of said front
booster piston and positioned in a front end portion of said piston boss,
said coupling cylinder including a bottom plate for coupling with said
piston boss;
a return coil spring elastically set between a front end wall of said
booster shell and said piston boss, for urging said piston boss in a
direction away from said front end of said booster shell; and
a reinforcing cylinder positioned in said coupling cylinder, said coupling
cylinder integrally formed with said front booster piston,
wherein said reinforcing cylinder includes an inward flange at a front end
thereof, said inward flange being biased by a rear end of said return coil
spring for holding said reinforcing cylinder on said bottom plate of said
coupling cylinder at a predetermined contact position,
wherein said booster further comprises a plurality of ribs positioned on an
inner cylindrical surface of said reinforcing cylinder, wherein said ribs
extend radially from said inward flange,
said ribs being coupled to a rear surface of said inward flange.
3. A tandem type vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss for engaging said front booster piston;
a coupling cylinder extending from an inner peripheral edge of said front
booster piston and positioned in a front end portion of said piston boss,
said coupling cylinder including a bottom plate for coupling with said
piston boss;
a return coil spring elastically set between a front end wall of said
booster shell and said piston boss, for urging said piston boss in a
direction away from said front end of said booster shell; and
a reinforcing cylinder positioned in said coupling cylinder, said coupling
cylinder integrally formed with said front booster piston,
wherein said reinforcing cylinder includes an inward flange at a front end
thereof, said inward flange being biased by a rear end of said return coil
spring for holding said reinforcing cylinder on said bottom plate of said
coupling cylinder at a predetermined contact position,
wherein said inward flange includes an annular protrusion, said annular
protrusion for engaging the rear end of said return coil spring.
4. A tandem type vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss for engaging said front booster piston;
a coupling cylinder extending from an inner peripheral edge of said front
booster piston and positioned in a front end portion of said piston boss,
said coupling cylinder including a bottom plate for coupling with said
piston boss;
a return coil spring elastically set between a front end wall of said
booster shell and said piston boss, for urging said piston boss in a
direction away from said front end of said booster shell; and
a reinforcing cylinder positioned in said coupling cylinder, said coupling
cylinder integrally formed with said front booster piston,
wherein said reinforcing cylinder includes an inward flange at a front end
thereof, said inward flange being biased by a rear end of said return coil
spring for holding said reinforcing cylinder on said bottom plate of said
coupling cylinder at a predetermined contact position,
said booster further comprises an annular protrusion comprising a
prolongation of the front end of said reinforcing cylinder, said annular
protrusion being rigidly attached to the rear end of said return coil
spring on an inner cylindrical surface thereof.
5. The tandem type vacuum booster of claim 1, further comprising a front
diaphragm positioned on a rear surface of said from booster piston, said
front diaphragm including an inner peripheral bead positioned between said
front booster piston and said piston boss.
6. The tandem type vacuum booster of claim 1, further comprising an output
rod coupled to said piston boss, said output rod protruding from said
piston boss in a direction toward said front end.
7. A tandem type vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss for engaging said front booster piston;
a coupling cylinder extending from an inner peripheral edge of said front
booster piston and positioned in a front end portion of said piston boss,
said coupling cylinder including a bottom plate for coupling with said
piston boss;
a return coil spring elastically set between a front end wall of said
booster shell and said piston boss, for urging said piston boss in a
direction away from said front end of said booster shell; and
a reinforcing cylinder positioned in said coupling cylinder, said coupling
cylinder integrally formed with said front booster piston,
wherein said reinforcing cylinder includes an inward flange at a front end
thereof, said inward flange being biased by a rear end of said return coil
spring for holding said reinforcing cylinder on said bottom plate of said
coupling cylinder at a predetermined contact position,
said booster further comprising an output rod coupled to said piston boss,
said output rod protruding from said piston boss in a direction toward
said front end,
wherein said inward flange includes an inner peripheral surface for
supporting said output rod at a middle portion of said output rod.
8. The tandem type vacuum booster of claim 7, wherein said inward flange
includes a plurality of holes formed therein.
9. The tandem type vacuum booster of claim 1, wherein said piston boss is
integrally formed with a cylindrical valve case for accommodating a
control valve.
10. The tandem type vacuum booster of claim 1, further comprising
connecting means for connecting said piston boss to said bottom plate,
wherein said reinforcing cylinder is positioned so as to surround said
connecting means.
11. A vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss coupled to said front booster piston;
a first cylinder extending from an edge of said front booster piston
positioned in a front end portion of said piston boss, said first cylinder
including a plate for coupling with said piston boss;
means for connecting said piston boss to said plate;
a return coil spring for urging said piston boss in a direction away from
said front end; and
a second cylinder positioned in said first cylinder,
wherein said second cylinder includes an inward flange at a front end
thereof for reinforcing said second cylinder and for holding said return
coil spring, said second cylinder being positioned so as to surround said
connecting means; and
second cylinder being held in said first cylinder solely by said return
coil spring.
12. The vacuum booster of claim 11, wherein said return coil spring is in
contact with said inward flange and said return coil spring urging said
inward flange against said plate.
13. A vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss coupled to said front booster piston;
a first cylinder extending from an edge of said front booster piston
positioned in a front end portion of said piston boss, said first cylinder
including a plate for coupling with said piston boss;
means for connecting said piston boss to said plate;
a spring for urging said piston boss in a direction away from said front
end;
a second cylinder positioned in said first cylinder, wherein said second
cylinder is positioned so as to surround said connecting means; and
retaining means for retaining said second cylinder in a predetermined
position on said plate,
wherein said retaining means is separately formed from said connecting
means,
said second cylinder includes an inward flange at a front end thereof,
said retaining means comprises a rear end of said spring being in contact
with said inward flange and said rear end of said spring urging said
inward flange against said plate,
a plurality of ribs positioned on an inner cylindrical surface of said
second cylinder, wherein said ribs extend radially from said inward
flange.
14. The vacuum booster of claim 13, wherein said ribs are formed on a rear
surface of said inward flange.
15. A vacuum booster comprising:
a booster shell having a front end;
a front booster piston reciprocating back and forth in said booster shell;
a piston boss coupled to said front booster piston;
a first cylinder extending from an edge of said front booster piston
positioned in a front end portion of said piston boss, said first cylinder
including a plate for coupling with said piston boss;
means for connecting said piston boss to said plate;
a spring for urging said piston boss in a direction away from said front
end;
a second cylinder positioned in said first cylinder, wherein said second
cylinder is positioned so as to surround said connecting means; and
an annular protrusion including a prolongation of the front end of said
second cylinder.
16. The vacuum booster of claim 15, wherein said annular protrusion is
rigidly attached to an inner cylindrical surface of a rear end of said
spring.
17. The vacuum booster of claim 11, wherein said second cylinder is
securedly positioned by an elastic force of said spring. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a tandem type vacuum booster which
operates a brake master cylinder or a clutch master cylinder on a motor
vehicle in a boost mode, and more particularly to an improvement of a
tandem type vacuum booster in which a piston boss integral with a
cylindrical valve case which accommodates a control valve is fastened with
screw members to the bottom plate of a coupling cylinder which is extended
from the inner peripheral edge of a front booster piston and set in the
front end portion of the piston boss, the inner peripheral bead of a front
diaphragm which is laid on the rear surface of the front booster piston is
inserted between the booster piston and the piston boss, a return coil
spring is elastically set between the front end wall of a booster shell
and the piston boss, to urge the piston boss backwardly, and an output rod
is coupled to the piston boss in such a manner that the output rod is
protruded forwardly of the piston boss.
A tandem type vacuum booster of this type has been well known in the
background art, for instance, by Examined Japanese Utility Model
Publication No. Hei. 4-17415.
If, in the tandem type vacuum booster, a coupling cylinder extended from
the inner peripheral edge of a front booster piston is low in rigidity,
then the coupling cylinder may be deformed during boost operation. The
deformation of the coupling cylinder, adversely affecting various
components, may lower the air-tightness of sealing members such as the
inner peripheral bead of the front diaphragm.
Hence, in the conventional tandem type vacuum booster, the front booster
piston and the coupling cylinder are made of a thick steel plate so that
the coupling cylinder is sufficiently high in rigidity. However, the use
of the thick steel plate for formation of the front booster piston results
in an undesirable increase in weight of the booster.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a tandem type vacuum
booster simple in construction in which a coupling cylinder is effectively
increased in rigidity, thereby to avoid an undesirable increase in weight
of the booster.
In order to achieve the foregoing object of the present invention, a first
aspect of the present invention resides in that, the tandem type vacuum
booster provides a booster shell, a front booster piston reciprocating
back and forth in the booster shell, a piston boss engaging with the front
booster piston, a coupling cylinder extended from an inner peripheral edge
of the front booster piston to be set in a front end portion of the piston
boss, the coupling cylinder including a bottom plate for fastening the
piston boss, a return coil spring elastically set between a front end wall
of the booster shell and the piston boss, for urging the piston boss
backwardly, and a reinforcing cylinder fitted in the coupling cylinder
integral with the front booster piston, in which the reinforcing cylinder
includes an inward flange at a front end thereof, the inward flange being
pushed by a rear end of the return coil spring to hold the reinforcing
cylinder on the bottom plate of the coupling cylinder at a predetermined
contact position.
A second aspect of the present invention resides in that in the tandem type
vacuum booster according to the first embodiment, an annular protrusion is
formed on the inward flange, the annular protrusion being engaged with the
rear end portion of the return coil spring.
A third aspect of the present invention resides in that, in the tandem type
vacuum booster according to the first and second embodiments, the inward
flange has an inner peripheral surface which supports the output rod at
the middle.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a sectional side elevation showing an example of a tandem type
vacuum booster which constitutes a first embodiment of the present
invention;
FIG. 2 is a sectional view taken along line 2--2 in FIG. 1;
FIG. 3 is a sectional side elevation showing another example of the tandem
type vacuum booster, which constitutes a second embodiment of the present
invention; and
FIG. 4 is a sectional view taken along line 4--4 in FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described with
reference to the accompanying drawings.
A first embodiment of the present invention will be described with
reference to FIGS. 1 and 2.
A brake master cylinder M, which is operated by a tandem type vacuum
booster B, is mounted on the front surface of the booster shell 1 of the
booster B. The booster shell 1 provides: a pair of shell halves, namely,
front and rear shell halves 1a and 1b which are combined with each other
through their confronted edges, thus defining a chamber; and a partition
board 1c set between the front and rear shell halves 1a and 1b to divide
the chamber into a front shell chamber 2 and a rear shell chamber 3. The
rear shell half 1b is supported by the vehicle body (not shown).
The front shell chamber 2 is divided into a front vacuum chamber 2a and a
front operating chamber 2b located behind the former 2a by a front booster
piston 4 which is reciprocated back and forth in the shell chamber, and by
a front diaphragm 5 which is bonded to the rear surface of the front
booster piston 4 and held between the front shell half 1a and the
partition board 1c. Similarly, the rear shell chamber 3 is divided into a
rear vacuum chamber 3a and a rear operating chamber 3b located behind the
former 3a by a rear booster piston 6 which is reciprocated back and forth
in the rear shell chamber, and by a rear diaphragm 7 which is bonded to
the rear surface of the rear booster piston 6 and fixedly held between the
two shell halves 1a and 1b together with the partition board 1c.
The front and rear booster pistons 4 and 6 are annular and made of a steel
plate. Those booster pistons 4 and 6 are coupled to both end portions of a
piston boss 10 of synthetic resin, which is slidably supported through a
bushing 8 and a seal member 9 on the partition board 1c, as follows:
A round recess 11 is formed in the front end face of the piston boss 10 to
the depth which is about a half of the length of the piston boss 10. The
piston boss 10 has a flange 12 on the outer cylindrical surface which is
located slightly away from the rear end. A coupling cylinder 13 with an
bottom plate 13a, which is extended from the inner peripheral edge of the
front booster piston 4, is fitted in the round recess 11. A retaining
plate 14 is set on the rear end face of the piston boss 10, to hold the
rear booster piston 6 with the aid of the aforementioned flange 12. The
retaining plate 14, the piston boss 10, and the bottom plate 13a are
secured to one another with a plurality of through-bolts (three
through-bolts in the case of FIG. 1) 15 and nuts 16 engaged with the
former 15.
The inner peripheral bead 5a of the front diaphragm 5, and an annular
retainer 17 are set between the front booster piston 4 and the front end
face of the piston boss 10 in such a manner that the retainer 17 covers
the outer cylindrical surface and the rear surface of the inner peripheral
bead 5a. The inner peripheral bead 7a of the rear diaphragm 7 is set
between the flange 12 and the retaining plate 14 in such a manner that it
covers the inner peripheral end of the rear booster piston 6. Hence, the
front booster piston 4, the rear booster piston 6, and the piston boss 10
are combined into one unit, and the inner peripheral beads 5a and 7a of
the diaphragms 5 and 7 are fixedly secured to the booster pistons 4 and 6,
respectively.
The piston boss 10 has bolt holes 18 into which the through-bolts 15 are
inserted. Seal members 19 are fitted in the bolt holes 18, to prevent the
communication between the front vacuum chamber 2a and the rear operating
chamber 3b. A seal member 20 is set between the aforementioned bottom
plate 13a and the piston boss 10 in such a manner that it surrounds the
through-bolts 15, which prevents the communication between first and
second forked ports 30 and 31 (described later) through the gap between
the bottom plate 13a and the piston boss 10.
The through-bolts 15 have rectangular heads 15a, which are set on the side
of the rear operating chamber 3b. More specifically, the rectangular heads
15a are engaged with recesses 21 formed in the retaining plate 14 which
are similar in configuration to the rectangular heads 15a, so that the
rotation of the rectangular heads 15a and accordingly the through-bolts 15
is prevented, Hence, on the side of the front vacuum chamber 2a, the nuts
16 can be positively engaged with the through-bolts 15.
A reinforcing cylinder 22 of synthetic resin for reinforcing the coupling
cylinder 13 is fitted in the coupling cylinder 13 in such a manner that it
surrounds the nuts 16. The length of the reinforcing cylinder 22 is longer
than half of the length of the coupling cylinder 13. The rear end of the
reinforcing cylinder 22 is abutted against the bottom plate 13a of the
coupling cylinder 13. Furthermore, the reinforcing cylinder 22 has an
annular inward flange 22a which is extended radially inwardly from the
front edge in such a manner as to cover the front end portions of the
through-bolts 15 and the nuts 16. A plurality of ribs 22b are formed on
the inner cylindrical surface of the reinforcing cylinder 22 in such a
manner that they are extended radially and are coupled to the rear surface
of the inward flange 22a. The inward flange 22a and the ribs 22b assure
the rigidity of the reinforcing cylinder 22.
An annular protrusion 22c is formed on the front surface of the inward
flange 22. The annular protrusion 22c is press-fitted in the rear end
portion of a return coil spring 23, which is elastically set between the
front shell half 1a and the inward flange 22a. The piston boss 10, and
accordingly the booster pistons 4 and 6 are kept urged backwardly by the
elastic force of the return coil spring 23. The backward movement of the
booster pistons 4 and 6 is limited by a number of protrusions 24 formed on
the rear surface of the rear diaphragm 6; that is, the backward movement
is allowed until the protrusions 24 abut against the rear wall of the
booster shell 1.
A cylindrical valve case 25 is protruded from the rear end of the piston
boss 10. The cylindrical valve case 25 is slidably supported through a
bushing 27 and a seal member 28 by a rear elongated cylinder 26 which is
extended from the rear end of the rear shell half 1b.
The front vacuum chamber 2a is connected through a negative pressure
introducing pipe 29 to a negative pressure source (such as the inside of
the suction manifold of an internal combustion engine), and is
communicated with the rear vacuum chamber 3a through a first forked port
30 formed in the piston boss 10. The front and rear operating chambers 2b
and 3b are communicated with each other through a second forked port 31
formed in the piston boss 10. Furthermore, the front and rear operating
chambers 2b and 3b are communicated alternately with the front and rear
vacuum chambers 2a and 3a and an air introducing hole 33 formed in the
bottom plate 26a of the rear elongated cylinder 26 by means of a control
valve 32.
An input rod 35 coupled to a brake pedal 34, and the aforementioned control
valve 32 which is controlled by the input rod 35, are provided in the
cylindrical valve case 35 as follows: That is, a valve piston 38 is
slidably engaged with the front portion of the cylindrical valve case 25,
and the front end portion of the input rod 35 extended through the air
introducing hole 33 is rockingly coupled to with the valve piston 38. A
first valve seat 40.sub.1, which is annular, is protruded from the inner
cylindrical surface of the cylindrical valve case 25 in such a manner that
it surrounds a second valve seat 40.sub.2, which is also annular and
formed on the rear end face of the valve piston 38. A valve body 41
cooperating with those valve seats 40.sub.1 and 40.sub.2 is provided
inside the cylindrical valve case 25. The valve body 41 is made of rubber,
and it is in the form of a cylinder with both ends opened. The rear end
portion of the valve body 41, namely, a base end portion 41a is held in
close contact with the inner cylindrical surface of the cylindrical valve
case 25 with the aid of a holding cylinder 42 fitted in the latter 25. The
valve body 41 provides: a flexible portion 41b which is relatively thin
and is bent radially inwardly; and a valve portion 41c which is relatively
thick and integral with the front end of the flexible portion 41b. The
valve portion 41c is arranged confronted with the aforementioned first and
second valve seats 40.sub.1 and 40.sub.2.
The valve portion 41c is moved back and forth as the flexible portion 41b
deforms. More specifically, when moved forwardly, the valve portion 41c is
set on the first and second valve seats 40.sub.1 and 40.sub.2 ; and when
moved backwardly, it is received by the front end of the holding cylinder
42.
An annular reinforcing plate 43 is buried in the valve portion 41c, and a
valve spring 44 is elastically set between the reinforcing plate 43 and
the input rod 35, to urge the valve portion 41c towards the first and
second valve seats 40.sub.l and 40.sub.2.
Both one end of the first forked port 30, and one end of the second forked
port 31 are opened in the inner surface of the cylindrical valve case 25.
More specifically, the one end of the first forked port 30 is opened
outside the first valve seat 40.sub.1, and the one end of the second
forked portion 31 is opened inside the same valve seat 40.sub.1.
The inside of the second valve seat 40.sub.2 is communicated with the air
introducing hole 33 through the valve body 41 and the holding cylinder 42.
The valve body 41, the valve spring 44, and the first and second valve
seats 40.sub.1 and 40.sub.2 form the control valve 32.
A return spring 45 is elastically set between the input rod 35 and the
holding cylinder 42, to urge the input rod 35 towards its rear limit
position.
The rear limit position of the input rod 35 is determined as follows: When
a stopper plate 46, which is threadably mounted on the input rod 35 so
that its position can be adjusted freely, abuts against the inner surface
of the bottom plate 26a of the rear elongated cylinder 26, the input rod
35 is at the rear limit position. Since the stopper plate 46 can be
shifted on the input rod 35 by turning it, the rear limit position of the
input rod 35 may be shifted back and forth by turning the stopper plate
46. After the rear limit position has been determined, the stopper plate
46 is fixed by tightening a lock nut 47 which is also threadably engaged
with the input rod 35. The stopper plate 46 has an air vent hole 48 so
that it may not close the air introducing hole 33.
In order to filter the air taken in the cylindrical valve case 25 through
the air introducing hole 33, air filters 49 are provided inside the
cylindrical valve case 25 in such a manner that they are mounted on the
input rod 35. The air filters 49 are flexible to the extent that they do
not obstruct the relative displacement of the input rod 35 and the
cylindrical valve case 25.
The piston boss 10 has a large cylinder hole 37 and a small cylinder hole
36. More specifically, the large cylinder hole 37 is opened in the front
end face of the piston boss 10 at the center, and one end of the small
cylinder hole 36 is opened to the large cylinder hole 37 and the other end
to the cylindrical valve case 25. A reaction piston 51, which is integral
with the above-described valve piston 38 or abuts against it, is slidably
engaged with the small cylinder hole 36. An elastic piston 50 and an
output piston 51 are slidable engaged with the large cylinder hole 37 in
such a manner that the elastic piston 50 is confronted with the reaction
piston 52 and the output piston 51 is set on the front surface of the
elastic piston 50. In order to prevent the output piston 51 from coming
off the large cylinder hole 37, the inner peripheral edge of the
above-described bottom plate 13a is extended over the opening of the large
cylinder hole 37.
An output rod 53 is extended from the front surface of the output piston
51, and it is coupled to the piston 55 of the aforementioned brake master
cylinder M.
The operation of the above-described embodiment will be described.
First, when the vacuum booster B is at rest, the input rod 35 is at the
rear limit position as shown in FIG. 1, and the control valve 32 is in the
neutral state that, with the valve portion 41c set on the first and second
valve seats 40.sub.1 and 40.sub.2, the front and rear operating chambers
2b and 3b are not communicated with the vacuum chambers 2a and 3a and the
air introducing hole 33. Hence, the negative pressure of the negative
pressure source, being supplied through the negative pressure introducing
pipe 29, is stored in the vacuum chambers 2a and 3a, and the negative
pressure, being suitably decreased by the outside air, is held in the
operating chambers 2b and 3b. Thus, weak forwarding forces are applied to
the front and rear booster pistons 4 and 6 which are due to the difference
in pressure between the front vacuum chamber 2a and the front operating
chamber 2b and the difference in pressure between the rear vacuum chamber
3a and the rear operating chamber 3b. The forwarding forces being in
balance with the elastic force of the return coil spring 23, the booster
pistons 4 and 6 are stopped slightly ahead of their rear limit positions.
It is assumed that, in order to brake the vehicle, the brake pedal 34 is
depressed (operated) to move the input rod 35 and the valve piston 38
forwardly. In this case, initially the booster pistons 4 and 6 are not in
operation, and therefore the second valve seat 40.sub.2 leaves the valve
portion 41c immediately, so that the operating chambers 2b and 3b are
communicated with the air introducing hole 33. As a result, the air is
quickly introduced into the operating chambers 2b and 3b through the air
introducing hole 33 and the second valve seat 40.sub.2 and the second
forked port 31. Hence, the pressure in the operating chambers 2b and 3b is
made higher than that in the vacuum chambers 2a and 3a. The pressure
differences thus formed provide strong forwarding forces to cause the
booster pistons 4 and 6 to move forwardly against the elastic force of the
return coil spring 23, so that the piston 55 of the brake master cylinder
M is moved forwardly through the output rod 53. Thus, when the brake pedal
34 is depressed, the brake master cylinder M is operated without delay;
that is, the vehicle is braked quickly.
In the braking operation, the valve piston 38 is moved forwardly together
with the input rod 35 to abut against the elastic piston 50 through the
reaction piston 52. The elastic piston 50, receiving the operating
reactions of the booster pistons 4 and 6, is expanded (deformed) towards
the small cylinder hole 36, thus applying part of the reactions to the
reaction piston 52. That force is fed back to the side of the brake pedal
34 through the valve piston 38 and the input rod 35. The above-described
effects of reaction allows the operator to feel the output of the output
rod 53; i.e., the magnitude of the braking force.
As the force of depression of the brake pedal 34 increases; that is, as the
input to the input rod 35 increases, the output of the output rod 53 is
increased. When the output exceeds a predetermined boost limit, the front
surface of the valve piston 38 is abutted against the piston boss 10, so
that the aforementioned input is transmitted to the output rod 53 through
the valve piston 38, the piston boss 10, the elastic piston 50 and the
output piston 51. Thus, the output rod 53 outputs the sum of the forward
force due to the pressure differences of the booster pistons 4 and 6 and
the forward force due to the input.
When the brake pedal 34 is released, the input rod 35 is moved backwardly
together with the valve piston 38 by the elastic force of the return
spring 45, while the second valve seat 40.sub.2 is engaged with the valve
portion 41c of the valve body 41, and the valve body 41 is greatly moved
away from the first valve seat 40.sub.1. As a result, the operating
chambers 2b and 3b are communicated with the vacuum chambers 2a and 3a,
and the pressure differences of the booster pistons 4 and 6 are
eliminated. Hence, the booster pistons 4 and 6 are moved backwardly by the
elastic force of the return coil spring 23, thus releasing the brake
master cylinder M.
When the input rod 35 is returned until the stopper plate 46 abuts against
the bottom plate 26a of the elongated cylinder 26; that is, when the input
rod 35 is moved backwardly to the rear limit position, the rear booster
piston 6 is returned until the protrusions 24 of the rear diaphragm 7 abut
against the rear wall of the booster shell 1; that is, it is returned to
the rear limit position. Hence, the first valve seat 40.sub.1 is engaged
with the valve body 41c, while the latter 41c is slightly moved away from
the second valve seat 40.sub.2. As a result, the air is introduced into
the operating chambers 2b and 3b, thus providing pressure differences.
When the booster pistons 4 and 6 are slightly moved forwardly by the
pressure differences, the gap between the second valve seat 40.sub.2 and
the valve portion 41c is eliminated, and the control valve 32 is placed in
the neutral state again. Thus, the negative pressure decreased by the air
is maintained in the operating chambers 2b and 3b, so that the vacuum
booster B is held at rest as shown in FIG. 1.
In the tandem type vacuum booster B, the reinforcing cylinder 22 of
synthetic resin is fitted in the coupling cylinder 13 extended from the
inner peripheral edge of the front booster piston 4, and the inward flange
22a is extended radially inwardly from the front edge of the reinforcing
cylinder 22 to reinforce the latter 22. Hence, the use of the reinforcing
cylinder 22 which is light and high in rigidity, effectively increases the
rigidity of the coupling cylinder 13, and can prevent the deformation of
the coupling cylinder 13 during boost operation of the front booster
piston 4. Hence, the difficulty is eliminated that the inner peripheral
bead 5a of the front diaphragm 5 and the seal member 20 are adversely
affected in seal characteristic by the deformation of the coupling
cylinder 13.
The inward flange 22a of the reinforcing cylinder 22 supports the rear end
portion of the return coil spring 23. Hence, the reinforcing cylinder 22
is held at the position where it is abutted against the bottom plate 13a
of the coupling cylinder 13, by the elastic force of the return coil
spring 23. Therefore, it is unnecessary to provide a particular mounting
member for the reinforcing cylinder 22.
Furthermore, the rear end portion of the return coil spring 23 is
press-fitted on the annular protrusion 22c formed on the front surface of
the inward flange 22a. Hence, the return coil spring 23 is prevented from
coming off the reinforcing cylinder 22 before the booster shell 1 is
assembled.
FIGS. 3 and 4 shows a second embodiment of the present invention.
In the second embodiment, an annular protrusion 22c is formed as a
prolongation of the front end portion of the reinforcing cylinder 22, and
the rear end portion of the return coil spring 23 is press-fitted in the
annular protrusion 22c. In this case, the effective length of the
reinforcing cylinder 22 is increased as much as the height of the annular
protrusion 22c, which further increases the rigidity of the coupling
cylinder 13.
The inward flange 22a of the reinforcing cylinder is so shaped that its
inner peripheral surface 22d supports the output rod 53 at the middle. The
inward flange 22a suppresses the vibration of the output rod 53, so that
the latter 53 is suitably held abutted against the piston 55 of the brake
master cylinder M, thus being able to transmit the thrust correctly. In
this case, in order that the inward flange 22a may not obstruct the
communication between the first forked port 30 and the front vacuum
chamber 2a, a plurality of through-holes 56 are formed in the inward
flange 22a.
In the second embodiment, the inner peripheral edge of the bottom plate 13a
of the coupling cylinder 13 is not extended towards the large cylinder
hole 37. Therefore, in order to prevent the output piston 51 from coming
off the large cylinder hole 37, the output rod 53 has a shoulder 53a at
the middle, which is set adjacent to the rear inner peripheral edge of the
inward flange 22a. In this case, after the coupling cylinder 13 is fixedly
secured to the piston boss 10 with the through-bolts 15 and the nuts 16,
the output piston 51 can be fitted in the large cylinder hole 37 of the
piston boss 10. That is, the nuts 16 can be tightened without being
obstructed by the output rod 53.
The other arrangements are equal to those in the first embodiment, and
accordingly in FIGS. 3 and 4, parts corresponding functionally to those
which have been described with reference to FIGS. 1 and 2 are therefore
designated by the same reference numerals or characters.
While there has been described in connection with the preferred embodiments
of the present invention, it will be obvious to those skilled in the art
that various changes and modifications may be made therein without
departing from the invention.
As described above, in the tandem type vacuum booster, according to the
present invention, the reinforcing cylinder of synthetic resin is fitted
in the coupling cylinder integral with the front booster piston, to
increase the rigidity of the coupling cylinder, and the reinforcing
cylinder has the inward flange at the front end which reinforces the
reinforcing cylinder, and which, being pushed by the rear end of the
return coil spring, is held on the bottom plate of the coupling cylinder.
Hence, the coupling cylinder is increased in rigidity by the reinforcing
cylinder which is light and high in rigidity; and the sealing members such
as the inner peripheral bead of the front diaphragm are air-tight without
a great increase of the weight. Furthermore, the reinforcing cylinder is
held in position by the elastic force of the return coil spring; that is,
it is unnecessary to provide a particular mounting member for it.
In the tandem type vacuum booster, the annular protrusion is formed on the
inward flange, and it is engaged with the rear end portion of the return
coil spring. Hence, the return coil spring is prevented from coming off
the reinforcing cylinder before the booster shell is assembled; that is,
the tandem type vacuum booster can be assembled with high efficiency.
Furthermore, in the tandem type vacuum booster, the inward flange is so
modified that it has the inner peripheral surface which supports the
output rod at the middle. Hence, the output rod is prevented from
vibration; that is, it is held stable at all times.
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