U.S. patent application number 09/814375 was filed with the patent office on 2001-10-04 for brake booster.
This patent application is currently assigned to Tokico, Ltd.. Invention is credited to Matsunaga, Kunihiro, Obata, Takuya, Takayama, Toshio.
Application Number | 20010025565 09/814375 |
Document ID | / |
Family ID | 18613825 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010025565 |
Kind Code |
A1 |
Takayama, Toshio ; et
al. |
October 4, 2001 |
Brake booster
Abstract
The present invention provides a brake booster that, although
simple in construction, capable of adjusting the braking force
derived by operation of a solenoid mechanism without worsening the
braking response. In the brake booster according to the present
invention, when a movable member (34) is shifted toward the rear
side by electromagnetic force of a solenoid (31), the shifting
movement is transmitted to a valve seat member (21) through pins
(50) to open an atmospheric valve (27) through which air is
introduced into a variable pressure chamber (9,10), whereby a
pressure difference is created between the variable pressure
chamber and a constant pressure chamber and generates booster
output (thrust output force). In the present invention, pressure in
the constant pressure chamber is introduced into a chamber (54)
formed at one end of the movable member (34) through a passage
(56), and atmosphere is introduced into a chamber (55) formed at
the other end of the movable member (34) through a passage (57),
thereby exerting on the movable member (34) a reaction force caused
by the pressure difference between the variable pressure chamber
and the constant pressure chamber. Thus, the booster output becomes
proportional to the electric current supplied to the solenoid (31).
Further in the present invention, the size of the passage (57) is
determined properly so as to limit air introduced therethrough into
the chamber (54) and keep the reaction force small until the
booster output reaches an adequately level, thereby preventing the
breaking response from deteriorating.
Inventors: |
Takayama, Toshio;
(Yamanashi-ken, JP) ; Matsunaga, Kunihiro;
(Yamanashi-ken, JP) ; Obata, Takuya;
(Yamanashi-ken, JP) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Tokico, Ltd.
|
Family ID: |
18613825 |
Appl. No.: |
09/814375 |
Filed: |
March 21, 2001 |
Current U.S.
Class: |
91/367 ;
91/370 |
Current CPC
Class: |
B60T 13/72 20130101;
B60T 13/575 20130101 |
Class at
Publication: |
91/367 ;
91/370 |
International
Class: |
F15B 013/16 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2000 |
JP |
2000-099478 |
Claims
What is claimed is:
1. A brake booster comprising: a housing; a power piston dividing
the interior of the housing into a constant pressure chamber and a
variable pressure chamber; a valve body supported by the power
piston; a plunger provided in the valve body for axial movement; an
input rod interconnecting a brake pedal and the plunger so that an
operation of the brake pedal is transmitted to the plunger to cause
its axial movement; a valve mechanism provided in the valve body
for controlling supply of operating fluid to the variable pressure
chamber in response to the axial movement of the plunger so that a
thrust output force is generated by pressure difference created
between the variable pressure chamber and the constant pressure
chamber based on the operation of the valve mechanism; an
electromagnetic biasing means including a movable member for
operating the valve mechanism independently from the operation of
the input rod, the movable member slidably provided in the valve
body; and a reaction force mechanism acting a reaction force on the
movable member according to pressure difference between the
variable pressure chamber and the constant pressure chamber,
wherein, the reaction force mechanism acts the reaction force on
the movable member so that an increasing rate of the thrust output
force is in accord with an increasing rate of the reaction
force.
2. A brake booster according to claim 1, wherein the valve
mechanism includes an operating fluid valve which, when opened,
permits the variable pressure chamber to communicate with a source
of the operating fluid, a vacuum valve which, when opened, permits
communication between the variable pressure chamber and the
constant pressure chamber, the plunger having a portion forming a
valve seat for the operating fluid valve, the movable member
engaging with a valve seat member of the vacuum valve so that the
movable member, when actuated, moves the valve seat member towards
a direction of closing the vacuum valve.
3. A brake booster according to claim 1, wherein the reaction force
mechanism has a pressure chamber formed at an end of the movable
member and at least one passage communicating the pressure chamber
with the variable pressure chamber, the passage designed its total
flow area at 0.5-10 square millimeters.
4. A brake booster according to claim 3, wherein the valve
mechanism includes an operating fluid valve which, when opened,
permits the variable pressure chamber to communicate with a source
of the operating fluid, a vacuum valve which, when opened, permits
communication between the variable pressure chamber and the
constant pressure chamber, the plunger having a portion forming a
valve seat for the operating fluid valve, the movable member
engaging with a valve seat member of the vacuum valve so that the
movable member, when actuated, moves the valve seat member towards
a direction of closing the vacuum valve.
5. A brake booster comprising: a housing; a power piston dividing
the interior of the housing into a constant pressure chamber and a
variable pressure chamber; a valve body supported by the power
piston; a plunger provided in the valve body for axial movement; an
input rod interconnecting a brake pedal and the plunger so that the
operation of the brake pedal is transmitted to the plunger to cause
its axial movement; a valve mechanism provided in the valve body
for controlling supply of operating fluid to the variable pressure
chamber in response to the axial movement of the plunger so that a
thrust output force is generated by pressure difference created
between the variable pressure chamber and the constant pressure
chamber based on the operation of the valve mechanism; an
electromagnetic biasing means including a movable member for
operating the valve mechanism independently from the operation of
the input rod, the movable member slidably provided in the valve
body; and a reaction force mechanism acting a reaction force on the
movable member according to pressure difference between the
variable pressure chamber and the constant pressure chamber,
wherein, the reaction force mechanism acts the reaction force on
the movable member so that the reaction force is created at the
same time or after the thrust output force is generated.
6. A brake booster according to claim 5, wherein the valve
mechanism includes an operating fluid valve which, when opened,
permits the variable pressure chamber to communicate with a source
of the operating fluid, a vacuum valve which, when opened, permits
communication between the variable pressure chamber and the
constant pressure chamber, the plunger having a portion forming a
valve seat for the operating fluid valve, the movable member
engaging with a valve seat member of the vacuum valve so that the
movable member, when actuated, moves the valve seat member towards
a direction of closing the vacuum valve.
7. A brake booster according to claim 5, wherein the reaction force
mechanism has a pressure chamber formed at an end of the movable
member and at least one passage communicating the pressure chamber
with the variable pressure chamber, the passage designed its total
flow area at 0.5-10 square millimeters.
8. A brake booster according to claim 7, wherein the valve
mechanism includes an operating fluid valve which, when opened,
permits the variable pressure chamber to communicate with a source
of the operating fluid, a vacuum valve which, when opened, permits
communication between the variable pressure chamber and the
constant pressure chamber, the plunger having a portion forming a
valve seat for the operating fluid valve, the movable member
engaging with a valve seat member of the vacuum valve so that the
movable member, when actuated, moves the valve seat member towards
a direction of closing the vacuum valve.
9. A brake booster comprising: a housing; a power piston dividing
the interior of the housing into a constant pressure chamber and a
variable pressure chamber; a valve body supported by the power
piston; a plunger provided in the valve body for axial movement; an
input rod interconnecting a brake pedal and the plunger so that the
operation of the brake pedal is transmitted to the plunger to cause
its axial movement; a valve mechanism provided in the valve body
for controlling supply of operating fluid to the variable pressure
chamber in response to the axial movement of the plunger so that a
thrust output force is generated by pressure difference created
between the variable pressure chamber and the constant pressure
chamber based on the operation of the valve mechanism; an
electromagnetic biasing means including a movable member for
operating the valve mechanism independently from the operation of
the input rod, the movable member slidably provided in the valve
body; and a reaction force mechanism acting a reaction force on the
movable member according to pressure difference between the
variable pressure chamber and the constant pressure chamber,
wherein, the reaction force mechanism is provided with a pressure
chamber formed at an end of the movable member and at least one
passage communicating the pressure chamber with the variable
pressure chamber, the passage having a limited flow area for
limiting introducing of operating fluid into the pressure
chamber.
10. A brake booster according to claim 9, wherein the valve
mechanism includes an operating fluid valve which, when opened,
permits the variable pressure chamber to communicate with a source
of the operating fluid, a vacuum valve which, when opened, permits
communication between the variable pressure chamber and the
constant pressure chamber, the plunger having a portion forming a
valve seat for the operating fluid valve, the movable member
engaging with a valve seat member of the vacuum valve so that the
movable member, when actuated, moves the valve seat member towards
a direction of closing the vacuum valve.
11. A brake booster according to claim 9, wherein the total flow
area of the passage is designed 0.5-10 square millimeters.
12. A brake booster according to claim 11, wherein the valve
mechanism includes an operating fluid valve which, when opened,
permits the variable pressure chamber to communicate with a source
of the operating fluid, a vacuum valve which, when opened, permits
communication between the variable pressure chamber and the
constant pressure chamber, the plunger having a portion forming a
valve seat for the operating fluid valve, the movable member
engaging with a valve seat member of the vacuum valve so that the
movable member, when actuated, moves the valve seat member towards
a direction of closing the vacuum valve.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a control-type brake
booster capable of automatically increasing and decreasing braking
power by electromagnetically operating an atmospheric valve or
vacuum valve.
[0002] An example of such a brake booster is disclosed in Japanese
Patent Laid-open No. 7-503214 (1995), in which a valve body
contains a solenoid mechanism with a member movable by applying
electricity to the solenoid of the solenoid mechanism, and a
movement of the movable member opens a to valve mechanism, which
may be an atmospheric valve or vacuum valve, independently of the
valve operation by movements of the input rod connected to the
brake pedal.
[0003] It has been desired that as is the braking power output from
a brake booster when its valve mechanism is operated by movements
of the input rod connected to the brake pedal, the braking power
output from a brake booster having the above-mentioned solenoid
mechanism can also be adjusted across a wide range when operated by
the activation of the solenoid mechanism.
[0004] However, in the above-mentioned conventional brake booster,
the solenoid mechanism merely functions to open the valve mechanism
to the degree determined by the magnitude of electric current
supplied to the solenoid, and no correlation (or proportional
relationship) exists between the magnitude of the electric current
supplied to the solenoid mechanism and the magnitude of the braking
power output from the brake booster.
[0005] As a makeshift measure to obtain a desired magnitude of
braking power from a brake booster when its solenoid mechanism is
operated is to control the operation of the solenoid mechanism
based on a feed-back signal indicating the braking power being
output from the brake booster, for instance, on an output signal
from a master cylinder pressure sensor provided for detecting
pressure of braking liquid output from the master cylinder.
[0006] However, since an additional sensor is required that
functions like the master cylinder pressure sensor to output a
signal indicating the braking power being output from the brake
booster, the entire system becomes more expensive.
SUMMARY OF THE INVENTION
[0007] The present invention aims to eliminate the drawbacks in the
above-mentioned conventional brake booster. An object of the
present invention is to provide a brake booster that, while being
simple in construction, can fully adjust the braking power across a
wide range when its solenoid mechanism is operated.
[0008] According to one aspect of the present invention, there is
provided a brake booster wherein an interior of a shell is divided
into a constant pressure chamber and a variable pressure chamber by
a power piston, and a valve mechanism for controlling supply of
operating fluid to the variable pressure chamber by a shifting
movement of a plunger connected to an input rod cooperating with a
brake pedal is provided within a valve body supported by the power
piston, so that a thrust force generated on the power piston by
pressure difference between the variable pressure chamber and the
constant pressure chamber based on an operation of the valve
mechanism is output as a booster output force (thrust output
force).
[0009] The brake booster further comprises an electromagnetic
biasing means having a movable member for operating the valve
mechanism independently from an operation of the input rod, and a
reaction force mechanism for applying reaction force corresponding
to the pressure difference between the variable pressure chamber
and the constant pressure chamber to the movable member, whereby
the reaction force mechanism applies the reaction force to the
movable member so that an increasing rate of the booster output
force is in accord with an increasing rate of the reaction force
applied to the movable member.
[0010] According to another aspect of the present invention, in a
brake booster having the electromagnetic biasing means mentioned
above and the reaction force mechanism mentioned above, the
reaction force mechanism applies the reaction force to the movable
member at the same time or with a delay after the booster outputs
force.
[0011] In the above two aspects of the present invention in which
the reaction force corresponding to the pressure difference between
the variable pressure chamber and the constant pressure chamber is
exerted on the movable member, the booster output force becomes
proportional to the magnitude of the electric current supplied to
the electromagnetic biasing mechanism. Further, since the reaction
force is exerted on the movable member so that the booster output
force increasing rate is in accord with the reaction force
increasing rate acting on the movable member, or, so that the
reaction force is created at the same time or after the booster
output force is generated, the booster output force generated is
not prevented by the reaction force.
[0012] In the present invention, the reaction force mechanism is
provided with at least one passage providing communication between
a pressure chamber formed at one end of the movable member and the
variable pressure chamber. The at least one passage has a limited
flow area for limiting air flowing into the pressure chamber.
Preferably, the total flow area of the passage is designed 0.5-10
square millimeters.
[0013] Limiting the flow area of the passage as above, the timing
of the reaction force exerted on the movable member is adjusted
properly, and thus a better response of automatic braking can be
established.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a partially enlarged sectional view showing a
brake booster of one embodiment according to the present invention
(a partial enlarged view of FIG. 2);
[0015] FIG. 2 is a partial sectional view showing the brake booster
of the same embodiment according to the present invention (a
partially enlarged view of FIG. 3);
[0016] FIG. 3 is a sectional view showing the brake booster of the
same embodiment of the present invention; and
[0017] FIG. 4 is an enlarged cross-sectional view of X-X line in
FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Now, a brake booster according to an embodiment of the
present invention will be explained with reference to FIGS. 1
through 4.
[0019] A brake booster shown on FIGS. 1 through 4 is a tandem type
and has a shell 1 which is divided into a front chamber and a rear
chamber by a center shell 2. These two respective chambers are
further divided into constant pressure chambers 7,8 and variable
pressure chambers 9,10 by power pistons 5,6 having diaphragms 3,4.
The power pistons 5,6 support a valve body 11 that comprises a
large diameter cup portion 11a and a small diameter cylindrical
portion 11b connected thereto. The valve body 11 is disposed such
that the cup portion 11a thereof sealingly and slidably passes
through the center shell 2, and that the cylindrical portion 11b
thereof sealingly and slidably passes through a cylindrical support
portion 1a arranged on the rear side of the shell 1 and extends
rearwardly of the support portion.
[0020] The valve body 11 is formed with a constant pressure passage
(negative pressure passage) 12 that provides communication between
the two constant pressure chambers 7 and 8 and between the constant
pressure chambers 7,8 and the inside of the cylindrical portion 11b
of the valve body 11. The valve body 11 is also formed with an
atmosphere passage 13 that provides communication between the two
variable pressure chambers 9 and 10 and between the two variable
pressure chambers 9,10 and the inside of the cylindrical portion
11b of the valve body 11. Negative pressure, e.g. negative pressure
from the engine, is introduced into the constant pressure chamber 7
shown on the left side (front side) of the Figures. The negative
pressure is also introduced into the constant pressure chamber 8
shown on the right side (rear side) of the Figures via the negative
pressure passage 12. On the other hand, the atmosphere is
introduced into the cylindrical portion 11b of the valve body 11
through a filter unit 14 having a silencing function. The
atmosphere is supplied into the two variable pressure chambers 9
and 10 through the atmosphere passage 13 by operation of valve
mechanism 15 (as described later).
[0021] The valve mechanism 15 is connected to an input rod 16
cooperating with a brake pedal (not shown), which comprises: a
plunger 18 slidable along a hollow guide 17 (as described later)
disposed in the valve body 11; an annular atmospheric valve seat 19
formed at rear end of the plunger 18; a cylindrical valve seat
member 21 slidably inserted into the valve body 11 via a seal
member 20; an annular negative pressure valve seat 22 formed at
rear end of the valve seat member 21, a poppet valve 26 whose
proximal end portion is fixed to the cylindrical portion 11b of the
valve body 11 by means of a ring member 23 and a pressing member 24
and which is usually biased to sit on the atmospheric valve seat 19
and the negative pressure valve seat 22 by means of a valve spring
25 held at one end thereof onto the input rod 16. The atmospheric
valve seat 19 and the annular inner portion formed at the distal
end of the poppet valve 26 resting thereon constitute an
atmospheric valve 27. The negative pressure valve seat 22 and the
annular outer portion formed at the distal end of the poppet valve
26 resting thereon constitute a vacuum valve 28. The atmosphere or
the negative pressure is selectably supplied into the two variable
pressure chambers 9,10 when the atmospheric valve 27 or the vacuum
valve 28 is opened, respectively. Meanwhile, a return spring 29 is
placed between the pressing member 24 and the input rod 16 (see
FIG. 2). The plunger 18 is forced so as to abut the atmospheric
valve seat 19 onto the poppet valve 26 by a biasing force of the
return spring 29 and the valve spring 25 during a rest state of the
brake booster.
[0022] A solenoid mechanism (electromagnetic biasing means) 30 is
disposed in the cup portion 11a of the valve body 11. The solenoid
mechanism 30 substantially comprises: a solenoid 31; a housing 32
containing the solenoid 31 therein; and an annular movable member
(an armature) 34 having a seal member 33 in the housing 32 (see
FIG. 1) and being slidably disposed in the housing 32. The housing
32 comprises: a double cylindrical shaped main body portion 35
containing the solenoid 31 therein; an extension cylindrical
portion 36 extending rearward from the rear end of the main body
portion 36; and a separating portion 37 separating the main body
portion 35 thereof from the extension cylindrical portion 36. While
the extension cylindrical portion 36 of the housing 32 is inserted
into the inner surface of the valve body 11 via a seal member 38,
and a flange portion 39 formed on the outer circumference surface
of the main body portion 35 rests on a step portion 40 formed on
the inner surface of the cup portion 11a of the valve body 11, the
housing 32 is restrained in its movement against the valve body 11
by biasing force of a return spring 41 disposed in the constant
pressure chamber 7 provided on the front side. An inner flange 5b
is provided on a cylindrical portion 5a of the power piston 5
provided on the front side (see FIG. 1) and is interposed between
the flange portion 39 and the step portion 40. Thus, the valve body
11 and the housing 32 move together in the axial direction. In FIG.
3, reference mark "W" is a wire for supplying electricity to the
solenoid 31. The wire "W" usually extends outside of the brake
booster via a connector (not shown) disposed in the front face of
the shell 1.
[0023] The hollow guide 17 is disposed inside of the main body 35
of the housing 32. The hollow guide 17 comprises a large end
portion 42 engaged with a step portion 35a of the main body 35 and
a small diameter axis portion 43 extending from the large end
portion 42 rearwardly through the separating portion 37 of the
housing 32 (see FIG. 2). The plunger 18 is slidably inserted into
the small diameter axis portion 43. A stop key 44 extending the
radial direction is inserted into the valve body 11 through the
atmosphere passage 13, and the distal end portion of the stop key
44 is connected to the plunger 18. The proximal end portion of the
stop key 44 is arranged to abut against a stopper plate 45 (see
FIG. 1) fixed on a cylindrical support portion 1a of the shell 1.
The maximum setback position of the plunger 18 is the position
where the stop key 44 abuts against the stopper plate 45. The stop
key 44 is also inserted through a opening (long face hole) 21a. The
valve seat member 21 is allowed to move relatively to the plunger
18 within the range where the stop key 44 is movable within the
opening 21a.
[0024] A reaction disk 46 and a large diameter proximal end portion
47a of an output rod 47 are disposed on the forward side of the
step portion 35a of the main body 35 of the housing 32. The distal
end portion of the output rod 47 is extended forwardly through the
front side of the shell 1 air-tightly. The distal end portion of
the output rod 47 is connected to and is simultaneously moved with
a piston of a master cylinder (not shown). Further, the proximal
end large diameter portion 47a of the output rod 47 and the
reaction disk 46 are restrained from coming out of the housing 32
by means of a retainer 48 press-fixed on the front end of the valve
body 11 by means of the return spring 41. A recess 42a is formed in
the front face of the large end portion 42 of the hollow guide 17.
A pressure receiving plate 49 is disposed in the recess 42a. A
depth of the recess 42a is designed slightly more than the
thickness of the pressure receiving plate 49. The front end of the
plunger 18 is located slightly forwardly from the bottom of the
recess 42a when the brake booster is in its rest state. A little
gap "S" (see FIG. 1) is formed between the pressure receiving plate
49 and the reaction disk 46 in such a state.
[0025] There are pins 50 one ends of which are inserted and fixed
into the movable member 34 of the solenoid mechanism 30 and the
other ends of which are inserted into through-holes 51 formed in
the separating portion 37 in the housing 32. The valve seat member
21 having the negative pressure valve seat 22 at its rear end is
urged forwardly by means of a spring 52 fixed to the plunger 18 at
its one end. The front end of the valve seat member 21 is normally
placed in abutment against the separating portion 37 in the housing
32. The through-holes 51 of the separating portion 37 of the
housing 32 are formed in alignment with the front end of the valve
seat member 21. The other ends of the pins 50 inserted into the
through-holes 51 face the valve seat member 21 with a small gap
therebetween. Further, the movable member 34 of the solenoid
mechanism 30 is moved rearwardly by energizing the solenoid 31,
whereby the pins 50 fixed to the movable member 34 move the valve
seat member 21 rearwardly against the urging force from the spring
52 and the valve spring 25. Consequently, the poppet valve 26 is
separated from the atmospheric valve seat 19 formed at the rear end
of the plunger 18. Thus, the atmospheric valve 27 opens
independently of the movement of the plunger 18, that is, the
movement of the input rod 16.
[0026] A seal member 53 held on the inner circumference of the
movable member 34 provides sealing between the movable member 34
and the hollow guide 17. The outer circumference of the movable
member 34 is sealed by the seal member 33 against the housing 32.
Thus, two pressure chambers 54 and 55 are formed at both ends of
the movable member 34 respectively. The pressure chamber 54 formed
on the front side of the movable member 34 communicates with the
constant pressure chamber 7 provided on the front side through a
passage 56 formed in the housing 32. The pressure chamber 55 formed
on the rear side of the movable member 34 communicates with the
variable pressure chambers 10,9 through a passage 57 formed in the
separating portion 37 of the housing 32.
[0027] Now, operation of the brake booster having the
above-mentioned construction will be explained.
[0028] The brake booster is installed in a vehicle (not shown) by
means of plural stud bolts 58 provided on the backside face of the
shell 1 (see FIG. 3), and a brake pedal (not shown) is connected to
the input rod 16 in this state. Further, a master cylinder (not
shown) is attached to the brake booster by means of a stud bolt 59
provided on the front side face of the shell 1. The output rod 47
is connected to a piston in the master cylinder in this state.
[0029] In the brake booster placed in the initial condition as
shown in the Figures (FIGS. 1 through 3), the constant pressure
chambers 7,8 and the variable pressure chambers 9,10 are both
subjected to the given (negative) pressure, and the atmospheric
valve 27 and the vacuum valve 28 are closed. In this condition,
when the brake pedal is depressed to urge the input rod 16, the
plunger 18 moves forward and separates the atmospheric valve seat
19 formed at the rear end thereof from the poppet valve 26, thereby
opening the atmospheric valve 27. As a result, air flows into the
variable pressure chambers 10,9 through the atmosphere passage 13,
thereby creating a pressure difference between the variable
pressure chambers 10,9 and the constant pressure chambers 7,8.
Consequently, the power pistons 5,6 advance to generate thrust
force which is transmitted to the output rod 47 through the valve
body 11 and starts the braking action. In this initial braking
condition, while the gap "S" between the pressure receiving plate
49 and the reaction disk 46 is being closed, so-called "jump-in"
occurs, and the booster output force increases irrespective of the
input force, thereby generating an adequate initial braking
force.
[0030] After the jump-in ends, part of the output reaction force
from the output rod 47 is transmitted back to the input rod 16
through the reaction disk 46, the pressure receiving plate 49 and
the plunger 18. When the output reaction force (from the output rod
47) generated by the advancement of the valve body 11, becomes
equal to the brake pedal pressing force, the atmospheric valve 27
is closed, thereby maintaining the booster output force. Further
from this condition, when the brake pedal pressing force is
increased or decreased to cause imbalance between the reaction
force based on the pressure difference and the brake pedal pressing
force, either the atmospheric valve 27 or the vacuum valve 28 is
opened again, so that the reaction force based on the pressure
difference becomes equal to the brake pedal pressing force, thereby
adjusting the pressure difference caused between the variable
pressure chambers 10,9 and the constant pressure chambers 7,8.
Accordingly, when the solenoid 31 is not energized, the brake pedal
pressing force is multiplied by a predetermined boost ratio,
resulting in that the brake booster is operated as a normal brake
booster.
[0031] In the automatic braking mode in which the solenoid 31 is
energized by the electric current supplied to the solenoid 31, the
electromagnetic force acts on the movable member 34 and shifts the
movable member 34 towards the rear side. At that time, the pressure
chamber 54 formed at the one end of the movable member 34 becomes
equal in pressure to the constant pressure chamber 7 through the
passage 56, and the pressure chamber 55 formed at the other end of
the movable member 34 becomes equal in pressure to the variable
pressure chamber 10 through the passage 57, gaps formed around the
pins 50 in the through-holes 51 and the atmosphere passage 13. If
the electric current supplied to the solenoid 31 increases, the
electromagnetic force acting on the movable member 34 exceeds the
total spring force of the spring 52 and the valve spring 25, and
the movable member 34 is shifted toward the rear side, whereby the
pin 50 fixed thereto moves the valve seat member 21 towards the
rear side. As a result of this, the poppet valve 26 is separated
from the atmospheric valve seat 19 formed at the rear end of the
plunger 18 to open the atmospheric valve 27, thereby introducing
air into the variable pressure chambers 10,9 and creating a
pressure difference between the variable pressure chambers 10,9 and
the constant pressure chambers 7,8. Consequently, the power pistons
5,6 advance and generate thrust force which is transmitted to the
output rod 47 through the valve body 11, thereby starting the
braking action.
[0032] When the air is introduced into the variable pressure
chambers 10,9, the air is also introduced into the pressure chamber
55 provided at the other end of the movable member 34 through the
passage 57 and the gaps around the pins 50 in the through-holes 51.
Thereby, a pressure difference force caused by a pressure
difference between the pressure chamber 55 and the pressure chamber
54 which is maintained at a negative pressure is created and acts
on the movable member 34. This pressure difference force acts as
the reaction force in the direction in which the movable member 34
is returned to the front side (i.e., the direction opposite to the
direction of the electromagnetic force acting on the movable member
34). As a result, when constant electric current is supplied to the
solenoid 31, that is, when constant electromagnetic force acts on
the movable member 34, the movable member 34 is returned to the
front side by means of the pressure difference force. At the moment
when the electromagnetic force acting on the movable member 34
becomes equal to (i.e., balanced with) the pressure difference
force, the shifting movement of the movable member 34 towards the
front side stops, thereby closing the atmospheric valve 27, and the
booster output force is maintained thereafter. Thus, two pressure
chambers 54,55 formed at both ends of the movable member 34
constitute a reaction force mechanism that exerts a reaction force
on the movable member 34 in proportion to the pressure difference
between the variable pressure chambers 7,8 and the constant
pressure chambers 9,10.
[0033] Further from this condition, if the electric current
supplied to the solenoid 31 is increased or decreased to cause
imbalance again between the electromagnetic force and the pressure
difference force, both forces acting on the movable member 34, the
movable member 34 is shifted again to balance the pressure
difference force and the electromagnetic force, resulting in that
either the atmospheric valve 27 or the vacuum valve 28 is opened,
thereby adjusting the pressure in the variable pressure chambers
9,10 in accordance with the magnitude of the electric current
supplied to the solenoid 31.
[0034] In this way, since the booster output force becomes
proportional to the electric current supplied to the solenoid 31,
by changing the electric current supplied to the solenoid 31 across
a wide range, the booster output force can be adjusted across a
wide range as well. Thus, it is not required to provide a sensor
like the master cylinder pressure sensor which was required in the
conventional techniques for controlling the booster output force at
desired levels. Therefore, the construction of the brake booster
can be simplified and the brake booster can be made cheaper.
[0035] In the control type brake booster that functions as
described above, if air is introduced into the pressure chamber 55
formed at the other end of the movable member 34 before air is
introduced into the variable pressure chambers 9,10, the pressure
difference force acting on the movable member 34 i.e. the reaction
force acting on the movable member 34, increases before an adequate
booster output force is generated. As a result, the atmospheric
valve 27 will be prevented from fully opening, causing a delay in
introducing an adequate amount of air into the variable pressure
chambers 9,10 and thus a delay in generating an adequate booster
output force. The delay will manifest itself as a poor response of
the automatic braking. To avoid that, according to the brake
booster of the present invention, the total passage area of the
passages 57 formed in the separating portion 37 of the housing 32
and the gaps around the pins 50 in the through-holes 51 (see FIG.
4) is made small so that the booster output force will increase at
the same rate as the reaction force acting on the movable member 34
increases, or so that an adequate reaction force will be created at
the same time or after the booster output force is generated.
Thereby, until a sufficient booster output force is generated in
response to the electric current supplied to the solenoid 31, the
atmospheric valve 27 is kept open widely, improving the braking
response. It is preferable that the total flow area of the passages
57 and the gaps around the pins 50 in the through-holes 51 is about
0.5-10 square millimeters.
[0036] In this way, since the brake booster of this invention is
constructed so that the booster output force increases at the same
rate as the reaction force acting on the movable member 34
increases, or so that an adequate reaction force is created at the
same time or after the booster output force is generated, thereby
improving the braking response in the automatic braking mode and
increasing the reliability of the brake booster.
[0037] The above embodiment has been described, using a tandem type
brake booster. It should however be appreciated that the present
invention can also be embodied in a so-called single type brake
booster having a single set of variable pressure chamber and
constant pressure chamber.
[0038] Further, in the above embodiment, the passages 57 formed in
the separating portion 37 of the housing 32 and the gaps around the
pins 50 in the through-holes 51 function to introduce air into the
pressure chamber 55. It should however be appreciated that only one
of the passages 57 formed in the separating portion 37 of the
housing 32 or the gaps around the pins 50 in the through-holes 51
may function to introduce air into the pressure chamber 55.
* * * * *