Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reissue Patent
1999-11-04
2001-09-18
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C188S356000
Reissue Patent
active
RE037373
ABSTRACT:
FIELD OF INVENTION
This invention relates to a vacuum servo apparatus and, more particularly, to a vacuum servo apparatus applied above all to a brake booster for a vehicle.
BACKGROUND OF THE INVENTION
Related Art
Heretofore, a vacuum assistor apparatus (also termed an negative pressure servo apparatus) has been adopted in a vehicle as a brake booster for reducing the operating force during braking.
The vacuum servo apparatus, in which the negative suction pressure of an engine or an negative pressure of a vacuum pump is used as a servo force and, using the pressure difference between this negative pressure and the atmospheric pressure, a force exceeding the foot pressure of a driver applied to a braking pedal is hydraulically applied to a braking device, is a most commonplace system as a brake booster.
In, for example, a German Patent DE 4405092C1, a vacuum servo apparatus having a mechanism producing “additional jumping”, in which, if a brake pedal actuating speed by a vehicle driver exceeds a threshold value, e.g., during rapid braking, a solenoid in a servo apparatus is excited for adding and generating an output other than the biasing force by a driver's input, in association with the driving or braking conditions, has been proposed.
Meanwhile, the “additional jumping” means a phenomenon in which an output value in terms of an output/input ratio of a vacuum servo is rapidly increased in the absence of the input increase.
FIG. 8
illustrates a prior art and is a partial cross-sectional view of a vacuum servo apparatus proposed in the above German Patent DE 4405092C1, taken along the input/output shaft of the vacuum servo apparatus.
Referring to
FIG. 8
, the vacuum servo apparatus includes, in addition to detection means, not shown, adapted for detecting the brake pedal pressing velocity by a driver, a power piston
622
slidable along an input/output shaft
699
under a differential pressure between the negative pressure and the atmospheric pressure, and an input rod
644
on which is applied the foot pressure by the driver. The power piston
622
and the input rod
644
are provided on the outer periphery of the apparatus and on the inner periphery of the apparatus (within the power piston
622
), respectively.
Along the axial line
699
, looking from the input towards the output, there are mounted a transmission member
641
, mutually interacting with the input rod
644
, a reaction disc
648
, abutted on the inner periphery and on the outer periphery thereof against the input rod
622
and against the power piston
622
, respectively, and mutually interacting with the input rod
622
, and an output rod
650
abutted against the reaction disc
648
and mutually interacting with the braking device. Between the outer periphery of the transmission member
641
and the power piston
622
, there is provided a solenoid coil
640
extending parallel to the axial line
699
, whereas, between the outer periphery of the transmission member
641
and the inner periphery of the solenoid coil, there is arranged a solenoid plunger
630
sucked towards the output under an electromagnetic force generated by the solenoid
640
. The solenoid plunger
630
has an atmospheric valve element
632
.
Between the outer periphery of the input rod
644
and the inner periphery of the power piston
622
, there are provided an atmospheric valve
624
and a negative pressure valve
611
. The atmospheric valve
624
is made up of a valve seat
660
retained by the power piston
622
and biased by a coil spring
700
towards an output side and the above-mentioned atmospheric valve element
632
facing the inner periphery of the output side end face of the valve seat
660
. The atmospheric valve element
632
is provided in the solenoid plunger
630
and is extended along the input/output shaft
699
. Between the atmospheric valve element
632
and the transmission member
641
is interposed a coil spring
638
. The negative pressure valve
611
is made up of the valve seat
660
and an negative pressure valve element
623
facing the outer periphery of the output side end face of the valve seat
660
and formed within the inside of the power piston
622
for encircling the outer periphery of the atmospheric valve element
632
.
It is only the surface formed on the reaction disc retainer
622
for facing the forward end face of the solenoid plunger
630
that operates as a stop for restricting movement of the atmospheric element
632
towards the output side. In addition, there is no clearance between the transmission member
641
and the reaction member
648
. Therefore, the opening degree of the atmospheric valve
624
is substantially equal to the initial distance between the forward end face of the solenoid plunger
630
and the face of the reaction disc retainer
622
facing the froward end face, that is a clearance shown in FIG.
6
. This distance corresponds to the maximum opening degree.
The operation of the vacuum servo apparatus shown in
FIG. 8
is explained by referring to
FIGS. 8 and 9
. In the graph of
FIG. 9
, showing the performance of the vacuum servo apparatus, lines a, c denote operating lines for usual braking and for the case in which the solenoid of the conventional vacuum servo apparatus is excited for supplementing and generating an output other than a biasing force imposed by the input.
If an input f
1
is applied by a driver on the input rod
644
, the vacuum servo apparatus generates an output a
1
. If, in the course of application of the input f
1
is applied, the solenoid in the servo apparatus is excited, as a result of detection of the emergency braking state or for other reasons, for supplementing and generating an output other than the biasing force by the input.
The solenoid plunger
630
is moved towards the output side under the electromagnetic force generated by the solenoid coil
640
so that the forward end face of the solenoid plunger
630
is abutted against a surface formed on the reaction disc retainer
622
for facing the forward end face. The atmospheric valve element
632
provided on the solenoid plunger
630
is also moved towards the output side for opening the valve
624
to permit atmospheric air to be intruded into a variable pressure chamber for generating a force of driving the power piston
622
towards the output side.
The reaction member
648
is elastically deformed by the thrusting force exerted by the power piston
622
for generating a force of reaction for thrusting back the input member
641
so that the input member
641
and the input rod
644
is moved towards the input side. However, since the atmospheric valve
632
is not moved towards the input side, the atmospheric valve
624
keeps on to be opened, so that the pressure within the variable pressure chamber reaches the atmospheric pressure. Thus the vacuum servo apparatus is in the maximum assisting state and generates an output c
1
. Subsequently, the vacuum servo apparatus operates on a line c.
That is, if current is supplied through the solenoid coil
640
at an input f
1
an output jumps at once to c
1
from an output a
1
under an additional jumping.
SUMMARY OF THE DISCLOSURE
Problem to be Solved by the Invention
However, the conventional vacuum servo apparatus, proposed in, for example, the above German Patent DE 4405092Cb1, has the following disadvantages.
Referring again to
FIGS. 8 and 9
, if the vacuum servo apparatus generates the output c
1
under the maximum biasing state, (that is with the atmospheric valve
624
being opened as a result of the solenoid coil
640
being fed with current, with the pressure in the pressure variation chamber reaching the atmospheric pressure), and the input amount applied to the input rod
644
is decreased for restoring the operation of the vacuum servo apparatus to the initial state, that is to the non-operating state, the vacuum servo apparatus keeps its maximum biasing state and continues to generate a high output c
2
, even if the input f is decreased to a value f
2
. The current supply to the solenoid coil
640
is interrupte
Miwa Akihiko
Tsubouchi Kaoru
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Butler Douglas C.
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