Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2002-09-03
2004-08-31
Lazo, Thomas E. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06782794
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a negative pressure boosting device used as a brake booster or the like and, more particularly, to a negative pressure boosting device capable of exhibiting ideal input-output characteristics by providing different servo ratios for a low input range and for a high input range, respectively.
Conventionally, a negative pressure boosting device utilizing negative pressure is used as a brake booster in an automobile such as a passenger car. As an example of conventional typical negative pressure boosting devices, a negative pressure boosting device as shown in
FIG. 4
is known. In
FIG. 4
, numeral
1
designates a negative pressure boosting device,
2
designates a front shell,
3
designates a rear shell,
4
designates a valve body,
5
designates a power piston comprising a power piston member
6
attached to the valve body
4
and a diaphragm
7
disposed between the shells
2
and
3
,
8
designates a constant pressure chamber which is formed in a space between the shells
2
and
3
and is defined by the power piston
5
and into which negative pressure is always introduced,
9
designates a variable pressure chamber which is formed in the space between the shells
2
and
3
and is defined by the power piston
5
and into which atmospheric pressure is introduced during operation,
10
designates a valve plunger,
11
designates an input shaft connected to a brake pedal (not shown),
12
designates a valve element,
13
designates a first valve seat which is annular and is formed on the valve body
4
,
14
designates a second valve seat which is annular and is formed on the valve plunger
10
,
15
designates a vacuum valve composed of the valve element
12
and the first valve seat
13
,
16
designates an atmospheric valve composed of the valve element
12
and the second valve seat
14
,
17
designates a valve spring always biasing the valve element
12
in such a direction as to seat the valve element
12
onto the first valve seat
13
,
18
designates an atmosphere inlet,
19
designates a vacuum passage,
20
designates a key member for restricting the movement of the valve plunger
10
relative to the valve body
4
to a predetermined value and defining the rear most positions of the valve body
4
and the valve plunger
10
,
21
designates a spacer,
22
designates a reaction disk,
23
designates an output shaft,
24
designates a return spring, and
25
designates a vacuum pressure inlet. The vacuum valve
15
and the atmospheric valve
16
compose a valve mechanism of the conventional example.
In the negative pressure boosting device
1
having the aforementioned structure, negative pressure is always introduced into the constant pressure chamber
8
through the vacuum pressure inlet
25
. In the inoperative state of the negative pressure boosting device
1
, the valve body
4
, the power piston
5
, the valve plunger
6
, the input shaft
11
, and the output shaft
23
are positioned as shown in FIG.
4
. In these positions, the vacuum valve
15
is open and the atmospheric valve
16
is closed. That is, the variable pressure chamber
9
is in communication with the constant pressure chamber
8
via the open vacuum valve
15
and the vacuum passage
19
and is isolated from the atmosphere. Therefore, negative pressure is introduced into the variable pressure chamber
9
so that there is no difference in pressure between the variable pressure chamber
9
and the constant pressure chamber
8
.
Upon depression of the brake pedal for normal braking operation, the input shaft
11
is moved forward to move the valve plunger
10
forward. Accordingly, the valve element
12
is seated on the first valve seat
13
and the second valve seat
14
is spaced apart form the valve element
12
so as to close the vacuum valve
15
and open the atmospheric valve
16
. That is, the variable pressure chamber
9
is isolated from the constant pressure chamber
8
and is in communication with the atmosphere. Therefore, the atmosphere is introduced into the variable pressure chamber
9
through the atmosphere inlet
18
and the open atmospheric valve
16
. The result is a difference in pressure between the variable pressure chamber
9
and the constant pressure chamber
8
. Because of the differential pressure, the power piston
5
is moved forward and the output shaft
23
is moved forward via the valve body
4
so as to move the piston of a master cylinder (not shown).
In the very initial stage of operation of the negative pressure boosting device
1
, the forward movement of the valve plunger
10
moves the spacer
21
, but the spacer
21
does not come in contact with the reaction disk
22
yet. Therefore, the reaction force is not transferred from the output shaft
23
to the brake pedal through the reaction disk
22
, the spacer
21
, the valve plunger
10
, and the input shaft
11
. As the input shaft
11
is further moved forward, the power piston
5
is also further moved forward so as to further move the piston of the master cylinder forward via the valve body
4
and the output shaft
23
. Then, the valve plunger
10
and the spacer
21
are also further moved forward so that the spacer
21
comes in contact with the reaction disk
22
. As a result, the reaction force is transferred from the output shaft
23
to the brake pedal through the reaction disk
22
, the spacer
21
, the valve plunger
10
, and the input shaft
11
. That is, the negative pressure boosting device
1
produces output corresponding to the input, thus exhibiting the jumping characteristic.
As the output of the negative pressure boosting device
1
reaches a predetermined value that is obtained by boosting the input of the input shaft
11
exerted with a pedaling force in accordance with a servo ratio, the atmospheric valve
16
and the vacuum valve
15
are both closed. In this state, the device becomes in the intermediate load state. Because of the output of the vacuum boosting device
1
, the master cylinder produces braking pressure so that the wheel cylinders produce relatively large braking force i.e. boosted pedaling force, thereby operating the service braking.
As the brake pedal is released to cancel the braking operation from the state where the negative pressure boosting device
1
is in operation so that the atmospheric valve
16
and the vacuum valve
15
are both closed, the input shaft
11
and the valve plunger
10
are both moved backward. Therefore, the second valve seat
14
presses the valve element
12
backward so that the valve element
12
is spaced apart from the first valve seat
13
so as to open the vacuum valve
15
. That is, the variable pressure chamber
9
is isolated from the atmosphere and is in communication with the constant pressure chamber
8
. Accordingly, the atmosphere in the variable pressure chamber
9
is discharged to the constant pressure chamber
8
through the open vacuum valve
15
and the vacuum passage
19
and is then discharged further form the constant pressure chamber
8
to a vacuum source (not shown) through the vacuum inlet
25
. As a result of this, by the spring force of the return spring
24
, the valve body
4
and the power piston
5
are moved backward to the inoperative position shown in FIG.
4
. According to the backward movement of the valve body
4
, the output shaft
23
is also moved backward because of the spring force exerted by the return spring of the piston of the master cylinder, thereby canceling the service braking.
As the negative pressure boosting device
1
becomes in the full load range in the state that the pedaling force is great, i.e. the input of the negative pressure boosting device
1
is great, the boosting action according to the servo ratio of the negative pressure boosting device
1
is no more conducted so that the increase in output of the negative pressure boosting device
1
is proportional to the input of the negative pressure boosting device.
The aforementioned input-output characteristics of the conventional typical negative pressure boo
Inoue Hidefumi
Takasaki Yoshiyasu
Bosch Automotive Systems Corporation
Lazo Thomas E.
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